Allow extra_outputs on go_proto_compile

[tingilee]

What version of rules_go are you using?

0.40.0

What version of gazelle are you using?

0.28.0

What version of Bazel are you using?

6.3.0rc1

Does this issue reproduce with the latest releases of all the above?

Yes

What operating system and processor architecture are you using?

MacOS M1 Ventura and Linux AMD

Any other potentially useful information about your toolchain?

What did you do?

See below.

What did you expect to see?

We have a custom plugin to generate enums .pb.go files from .proto files. For example.proto, we expect both
example_dbenum.pb.go and example.pb.go to be generated as Bazel provider outputs. Currently, only files with the same name and .pb.go file extensions are allowed. I'd like to propose adding attributes to allow outputting more w/ custom proto plugins.

What did you see instead?

[fmeum]

This sounds useful. Since you have a concrete application in mind, would you be interested in contributing this improvement (with some support from maintainers)?

[tingilee]

@fmeum I'd love to. Here's a patch that has worked for our monorepo: #3631 Could you take a look? Happy to add tests and address comments.