Fields of `bytes` should be percent-encoded as query parameters

[coryan]

To send query parameters of type "object" we serialize the object as JSON and send expand the parameters:

https://github.com/googleapis/google-cloud-rust/blob/0b3d43254520095682b9717643d0b37de218a371/generator/internal/rust/codec.go#L694-L702

The resulting code looks like so:

https://github.com/googleapis/google-cloud-rust/blob/0b3d43254520095682b9717643d0b37de218a371/src/generated/showcase/src/transport.rs#L115-L124

Consequently fields of type bytes are base64-encoded. Looking at how showcase works, it seems that these should be percent-encoded (which makes sense for query parameters).

[dbolduc]

https://cloud.google.com/iam/docs/reference/rest/v1/organizations.roles/delete#query-parameters

This makes me think gapic-showcase is wrong.

[coryan]

And the proto specification is really bytes, not just a string:

https://cloud.google.com/iam/docs/reference/rpc/google.iam.admin.v1#google.iam.admin.v1.DeleteRoleRequest

[dbolduc]

We should still clean this up, but it is not a bug in our code.

Blocked externally on: https://github.com/googleapis/gapic-showcase/issues/1593