Generate client library for Bigtable Admin

[coryan]

This is blocked by

• Builder names may need to include service name #666
• Support message types that are self referential #586

The generated code fails to compile:

cargo new --lib --vcs none src/generated/bigtableadmin/v2
go -C generator/ run ./cmd/sidekick generate -project-root .. -specification-source google/bigtable/admin/v2 -service-config google/bigtable/admin/v2/bigtableadmin_v2.yaml -output src/generated/bigtableadmin/v2

Then cargo build gives you:

error[E0428]: the name `GetIamPolicy` is defined multiple times
    --> src/generated/bigtableadmin/v2/src/builders.rs:2803:1
     |
1032 | pub struct GetIamPolicy(BigtableInstanceAdminRequestBuilder<iam_v1::model::GetIamPolicyRequest>);
     | ------------------------------------------------------------------------------------------------- previous definition of the type `GetIamPolicy` here
...
2803 | pub struct GetIamPolicy(BigtableTableAdminRequestBuilder<iam_v1::model::GetIamPolicyRequest>);
     | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `GetIamPolicy` redefined here
     |
     = note: `GetIamPolicy` must be defined only once in the type namespace of this module

and

error[E0391]: cycle detected when computing when `model::r#type::Aggregate` needs drop
    --> src/generated/bigtableadmin/v2/src/model.rs:6793:5
     |
6793 |     pub struct Aggregate {
     |     ^^^^^^^^^^^^^^^^^^^^
     |
     = note: ...which immediately requires computing when `model::r#type::Aggregate` needs drop again
note: cycle used when computing when `model::ColumnFamily` needs drop
    --> src/generated/bigtableadmin/v2/src/model.rs:5502:1
     |
5502 | pub struct ColumnFamily {
     | ^^^^^^^^^^^^^^^^^^^^^^^
     = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information