tfprotov5/tf5server: Ensure server options are passed through on startup (#153)

Reference: #152

Currently this functionality cannot implement unit testing without a larger refactoring effort as there is no way to retrieve the generated `ServeConfig` and `plugin.ServeConfig` inside the function. While refactoring that logic into an unexported function such as:

```go
func prepareServeConfigs(providerAddress string, providerServerFunc func() tfprotov5.ProviderServer, opts ...ServeOpt) (*ServeConfig, *plugin.ServeConfig, error)
```

Would be fairly straightforward, the `ServeConfig` itself implements all unexported fields which presents some tougher challenges with `go-cmp`:

```
	panic: cannot handle unexported field at {*tf5server.ServeConfig}.logger:
	"github.com/hashicorp/terraform-plugin-go/tfprotov5/tf5server".ServeConfig
consider using a custom Comparer; if you control the implementation of type, you can also consider using an Exporter, AllowUnexported, or cmpopts.IgnoreUnexported
```

This chooses instead to fix the implementation to match `tf6server`, rather than bundle all this unrelated work into the simple bug fix.

Previously:

```console
❯ TF_ACC=1 go test -timeout=1m -v ./internal/sdkv2provider
=== RUN   TestProvider
--- PASS: TestProvider (0.00s)
=== RUN   TestProvider_impl
--- PASS: TestProvider_impl (0.00s)
=== RUN   TestAccTests
=== RUN   TestAccTests/corner_user
{"@caller":"/Users/bflad/go/pkg/mod/github.com/hashicorp/[email protected]/internal/logging/protocol.go:21","@Level":"trace","@message":"Received request","@module":"sdk.proto","@timestamp":"2022-02-04T16:28:52.602080-05:00","EXTRA_VALUE_AT_END":null,"tf_proto_version":"5.2","tf_provider_addr":"","tf_req_id":"a24b8a29-628a-01c2-0516-08b260627109","tf_rpc":"GetProviderSchema"}
{"@caller":"/Users/bflad/go/pkg/mod/github.com/hashicorp/[email protected]/internal/logging/protocol.go:21","@Level":"trace","@message":"Calling downstream","@module":"sdk.proto","@timestamp":"2022-02-04T16:28:52.602157-05:00","EXTRA_VALUE_AT_END":null,"tf_proto_version":"5.2","tf_provider_addr":"","tf_req_id":"a24b8a29-628a-01c2-0516-08b260627109","tf_rpc":"GetProviderSchema"}
{"@caller":"/Users/bflad/go/pkg/mod/github.com/hashicorp/[email protected]/internal/logging/protocol.go:21","@Level":"trace","@message":"Called downstream","@module":"sdk.proto","@timestamp":"2022-02-04T16:28:52.602257-05:00","EXTRA_VALUE_AT_END":null,"tf_proto_version":"5.2","tf_provider_addr":"","tf_req_id":"a24b8a29-628a-01c2-0516-08b260627109","tf_rpc":"GetProviderSchema"}
{"@caller":"/Users/bflad/go/pkg/mod/github.com/hashicorp/[email protected]/internal/logging/protocol.go:21","@Level":"trace","@message":"Served request","@module":"sdk.proto","@timestamp":"2022-02-04T16:28:52.602299-05:00","EXTRA_VALUE_AT_END":null,"tf_proto_version":"5.2","tf_provider_addr":"","tf_req_id":"a24b8a29-628a-01c2-0516-08b260627109","tf_rpc":"GetProviderSchema"}
{"@caller":"/Users/bflad/go/pkg/mod/github.com/hashicorp/[email protected]/internal/logging/protocol.go:21","@Level":"trace","@message":"Received request","@module":"sdk.proto","@timestamp":"2022-02-04T16:28:52.666614-05:00","EXTRA_VALUE_AT_END":null,"tf_proto_version":"5.2","tf_provider_addr":"","tf_req_id":"97a74410-24d3-4d4e-c61c-9062200c75e8","tf_rpc":"GetProviderSchema"}
... many more ...
```

Now:

```console
❯ TF_ACC=1 go test -timeout=1m -v ./internal/sdkv2provider
=== RUN   TestProvider
--- PASS: TestProvider (0.00s)
=== RUN   TestProvider_impl
--- PASS: TestProvider_impl (0.00s)
=== RUN   TestAccTests
=== RUN   TestAccTests/corner_regions_cty
=== RUN   TestAccTests/corner_user
=== RUN   TestAccTests/corner_regions
=== RUN   TestAccTests/corner_bigint_data
=== RUN   TestAccTests/corner_bigint
=== RUN   TestAccTests/corner_user_cty
--- PASS: TestAccTests (6.76s)
    --- PASS: TestAccTests/corner_regions_cty (1.24s)
    --- PASS: TestAccTests/corner_user (1.02s)
    --- PASS: TestAccTests/corner_regions (0.92s)
    --- PASS: TestAccTests/corner_bigint_data (0.92s)
    --- PASS: TestAccTests/corner_bigint (0.97s)
    --- PASS: TestAccTests/corner_user_cty (1.69s)
PASS
ok      github.com/hashicorp/terraform-provider-corner/internal/sdkv2provider   7.510s
```

Author: bflad

.changelog/153.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+tfprotov5/tf5server: Ensure server options are passed through on startup
+```

tfprotov5/tf5server/server.go

@@ -259,6 +259,7 @@ func Serve(name string, serverFactory func() tfprotov5.ProviderServer, opts ...S
 		Plugins: plugin.PluginSet{
 			"provider": &GRPCProviderPlugin{
 				Name:         name,
+				Opts:         opts,
 				GRPCProvider: serverFactory,
 			},
 		},