GRPC docker samples failing

[vurhanau]

GRPC samples stopped working on ARM:

samples % export SAMPLE_DIR=Spiffe.Sample.Grpc.Tls
docker-compose -p spiffe-grpc-tls up -d --build

Compose can now delegate builds to bake for better performance.
 To do so, set COMPOSE_BAKE=true.
[+] Building 0.9s (12/14)                                                                                                                                           docker:desktop-linux
 => [server internal] load build definition from Dockerfile                                                                                                                         0.0s
 => => transferring dockerfile: 681B                                                                                                                                                0.0s
 => [server internal] load metadata for mcr.microsoft.com/dotnet/aspnet:9.0                                                                                                         0.1s
 => [server internal] load metadata for mcr.microsoft.com/dotnet/sdk:9.0                                                                                                            0.2s
 => [server internal] load .dockerignore                                                                                                                                            0.0s
 => => transferring context: 5.12kB                                                                                                                                                 0.0s
 => [server build-env 1/6] FROM mcr.microsoft.com/dotnet/sdk:9.0@sha256:bb42ae2c058609d1746baf24fe6864ecab0686711dfca1f4b7a99e367ab17162                                            0.0s
 => => resolve mcr.microsoft.com/dotnet/sdk:9.0@sha256:bb42ae2c058609d1746baf24fe6864ecab0686711dfca1f4b7a99e367ab17162                                                             0.0s
 => [server internal] load build context                                                                                                                                            0.0s
 => => transferring context: 2.76kB                                                                                                                                                 0.0s
 => [server server 1/3] FROM mcr.microsoft.com/dotnet/aspnet:9.0@sha256:1af4114db9ba87542a3f23dbb5cd9072cad7fcc8505f6e9131d1feb580286a6f                                            0.0s
 => => resolve mcr.microsoft.com/dotnet/aspnet:9.0@sha256:1af4114db9ba87542a3f23dbb5cd9072cad7fcc8505f6e9131d1feb580286a6f                                                          0.0s
 => CACHED [server server 2/3] WORKDIR /server                                                                                                                                      0.0s
 => CACHED [server build-env 2/6] WORKDIR /sample                                                                                                                                   0.0s
 => CACHED [server build-env 3/6] COPY Spiffe.Sample.Grpc.Tls/ ./                                                                                                                   0.0s
 => CACHED [server build-env 4/6] RUN dotnet restore                                                                                                                                0.0s
 => ERROR [server build-env 5/6] RUN dotnet publish Server/Server.csproj -c Release -o server                                                                                       0.7s
------                                                                                                                                                                                   
 > [server build-env 5/6] RUN dotnet publish Server/Server.csproj -c Release -o server:                                                                                                  
0.348   Determining projects to restore...                                                                                                                                               
0.493   All projects are up-to-date for restore.                                                                                                                                         
0.678 /root/.nuget/packages/grpc.tools/2.71.0/build/_protobuf/Google.Protobuf.Tools.targets(291,5): error MSB6006: "/root/.nuget/packages/grpc.tools/2.71.0/tools/linux_arm64/protoc" exited with code 139. [/sample/Server/Server.csproj]
------
failed to solve: process "/bin/sh -c dotnet publish Server/Server.csproj -c Release -o server" did not complete successfully: exit code: 1

Related: grpc/grpc#38538

[vurhanau]

Parent spiffe id should contain x509pop.

entries.json should be updated to:

{
    "entries":[
        {
            "parent_id": "spiffe://example.org/spire/agent/x509pop/cn/agent.example.com",
            "spiffe_id": "spiffe://example.org/client",
            "selectors": [{
                "type": "docker",
                "value": "label:org.example.workload:client"
            }]
        },
        {
            "parent_id": "spiffe://example.org/spire/agent/x509pop/cn/agent.example.com",
            "spiffe_id": "spiffe://example.org/server",
            "selectors": [{
                "type": "docker",
                "value": "label:org.example.workload:server"
            }]
        }
    ]
}

[vurhanau]

PR to fix agent id:
#379