feat: Docs (#15)

* feat: Docs

- Add docs for GCP Dynamic Host Plugin
- Remove references of instances group since we do not currently support this

go.mod

@@ -8,7 +8,6 @@ require (
 	github.com/google/go-cmp v0.6.0
 	github.com/googleapis/gax-go/v2 v2.13.0
 	github.com/hashicorp/boundary/sdk v0.0.47
-	github.com/hashicorp/go-secure-stdlib/parseutil v0.1.8
 	golang.org/x/oauth2 v0.22.0
 	google.golang.org/api v0.196.0
 )
@@ -25,9 +24,6 @@ require (
 	github.com/golang/groupcache v0.0.0-20210331224755-41bb18bfe9da // indirect
 	github.com/google/s2a-go v0.1.8 // indirect
 	github.com/googleapis/enterprise-certificate-proxy v0.3.3 // indirect
-	github.com/hashicorp/go-secure-stdlib/strutil v0.1.2 // indirect
-	github.com/hashicorp/go-sockaddr v1.0.5 // indirect
-	github.com/ryanuber/go-glob v1.0.0 // indirect
 	go.opencensus.io v0.24.0 // indirect
 	go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc v0.54.0 // indirect
 	go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.54.0 // indirect