feat: Ability to pass in a scope for certificate authentication

[hawksight]

Attempts to fix #153. Requires #152 first as this includes the fix for #151.

Tested locally with my setup:

2024-10-29T12:18:50.973Z [WARN]  ValidateProviderConfig from "provider[\"registry.terraform.io/venafi/venafi\"]" changed the config value, but that value is unused
2024-10-29T12:18:50.973Z [INFO]  provider.terraform-provider-venafi: Configuring venafi provider: tf_req_id=3791080c-596f-42a6-7290-0a45676e057f tf_rpc=Configure @caller=/Users/peter.fiddes/projects/venafi/terraform-provider-venafi/venafi/provider.go:221 @module=venafi tf_provider_addr=registry.terraform.io/Venafi/venafi timestamp=2024-10-29T12:18:50.973Z
2024-10-29T12:18:50.973Z [INFO]  provider.terraform-provider-venafi: User-Agent: hashicorp-terraform-by-venafi/nknown: @caller=/Users/peter.fiddes/projects/venafi/terraform-provider-venafi/venafi/provider.go:222 @module=venafi tf_provider_addr=registry.terraform.io/Venafi/venafi tf_req_id=3791080c-596f-42a6-7290-0a45676e057f tf_rpc=Configure timestamp=2024-10-29T12:18:50.973Z
2024-10-29T12:18:50.973Z [INFO]  provider.terraform-provider-venafi: Using `Venafi Trust Protection Platform` with url https://demo-1.tpp.peter-fiddes-gcp.jetstacker.net to issue certificate: tf_provider_addr=registry.terraform.io/Venafi/venafi tf_req_id=3791080c-596f-42a6-7290-0a45676e057f tf_rpc=Configure @caller=/Users/peter.fiddes/projects/venafi/terraform-provider-venafi/venafi/provider.go:285 @module=venafi timestamp=2024-10-29T12:18:50.973Z
2024-10-29T12:18:50.973Z [INFO]  provider.terraform-provider-venafi: Setting up TLS Configuration: tf_provider_addr=registry.terraform.io/Venafi/venafi tf_req_id=3791080c-596f-42a6-7290-0a45676e057f tf_rpc=Configure @caller=/Users/peter.fiddes/projects/venafi/terraform-provider-venafi/venafi/provider.go:398 @module=venafi timestamp=2024-10-29T12:18:50.973Z
2024-10-29T12:18:51.058Z [INFO]  provider.terraform-provider-venafi: vCert: Got 200 OK status for GET https://demo-1.tpp.peter-fiddes-gcp.jetstacker.net/vedsdk/: timestamp=2024-10-29T12:18:51.058Z
2024-10-29T12:18:51.058Z [INFO]  provider.terraform-provider-venafi: PFX certificate provided for authentication, getting access token: @module=venafi tf_provider_addr=registry.terraform.io/Venafi/venafi tf_req_id=3791080c-596f-42a6-7290-0a45676e057f tf_rpc=Configure @caller=/Users/peter.fiddes/projects/venafi/terraform-provider-venafi/venafi/provider.go:456 timestamp=2024-10-29T12:18:51.058Z
2024-10-29T12:18:51.192Z [INFO]  provider.terraform-provider-venafi: vCert: Got 200 OK status for POST https://demo-1.tpp.peter-fiddes-gcp.jetstacker.net/vedauth/authorize/certificate: timestamp=2024-10-29T12:18:51.192Z
2024-10-29T12:18:51.264Z [INFO]  provider.terraform-provider-venafi: vCert: Got 200 OK status for GET https://demo-1.tpp.peter-fiddes-gcp.jetstacker.net/vedsdk/Identity/Self: timestamp=2024-10-29T12:18:51.264Z
2024-10-29T12:18:51.264Z [INFO]  provider.terraform-provider-venafi: Successfully authenticated: tf_req_id=3791080c-596f-42a6-7290-0a45676e057f tf_rpc=Configure @caller=/Users/peter.fiddes/projects/venafi/terraform-provider-venafi/venafi/provider.go:467 @module=venafi tf_provider_addr=registry.terraform.io/Venafi/venafi timestamp=2024-10-29T12:18:51.264Z
2024-10-29T12:18:51.266Z [DEBUG] ReferenceTransformer: "venafi_policy.team[\"team-1\"]" references: []
2024-10-29T12:18:51.266Z [DEBUG] ReferenceTransformer: "venafi_policy.team[\"team-2\"]" references: []
2024-10-29T12:18:51.266Z [DEBUG] ReferenceTransformer: "venafi_policy.team[\"team-3\"]" references: []
venafi_policy.team["team-3"]: Refreshing state... [id=\VED\Policy\Terraform\team-3]
venafi_policy.team["team-2"]: Refreshing state... [id=\VED\Policy\Terraform\team-awesome]
venafi_policy.team["team-1"]: Refreshing state... [id=\VED\Policy\Terraform\team-1]
2024-10-29T12:18:51.275Z [DEBUG] provider.stdio: received EOF, stopping recv loop: err="rpc error: code = Unavailable desc = error reading from server: EOF"
2024-10-29T12:18:51.276Z [INFO]  provider: plugin process exited: plugin=/Users/peter.fiddes/projects/venafi/terraform-provider-venafi/terraform-provider-venafi id=71371
2024-10-29T12:18:51.276Z [DEBUG] provider: plugin exited
2024-10-29T12:18:51.276Z [DEBUG] no planned changes, skipping apply graph check
2024-10-29T12:18:51.276Z [INFO]  backend/local: plan operation completed
2024-10-29T12:18:51.276Z [INFO]  backend/local: writing plan output to: plan

No changes. Your infrastructure matches the configuration.

Terraform has compared your real infrastructure against your configuration and found no differences, so no changes are needed.

I have tested the following other scenarios:

1. Define VENAFI_TOKEN, VENAFI_CLIENT_ID & VENAFI_SCOPE explicitly in provider. All works with token.
2. Define VENAFI_TOKEN and leave clientID and scope to the code default values. All still works with token.