feat(build): Add CodeGenBuilder (#1154)

This commit adds a new `CodeGenBuilder` that replaces the
client/server generate fn with a builder stlye that allows
adding config items in an non-breaking way. This also deprecates
both of the client/server generate fn in favor of the builder ones.

tonic-build/src/client.rs

@@ -9,6 +9,7 @@ use quote::{format_ident, quote};
 ///
 /// This takes some `Service` and will generate a `TokenStream` that contains
 /// a public module with the generated client.
+#[deprecated(since = "0.8.3", note = "Use the CodeGenBuilder::generate_client")]
 pub fn generate<T: Service>(
     service: &T,
     emit_package: bool,
@@ -16,6 +17,25 @@ pub fn generate<T: Service>(
     compile_well_known_types: bool,
     build_transport: bool,
     attributes: &Attributes,
+) -> TokenStream {
+    generate_internal(
+        service,
+        emit_package,
+        proto_path,
+        compile_well_known_types,
+        build_transport,
+        attributes,
+        &HashSet::default(),
+    )
+}
+
+pub(crate) fn generate_internal<T: Service>(
+    service: &T,
+    emit_package: bool,
+    proto_path: &str,
+    compile_well_known_types: bool,
+    build_transport: bool,
+    attributes: &Attributes,
     disable_comments: &HashSet<String>,
 ) -> TokenStream {
     let service_ident = quote::format_ident!("{}Client", service.name());