refactor: migrate to connectrpc/connect-go

[craigpastro]

This PR

Migrate from bufbuild/connect-go to connectrpc/connect-go.

Part of open-feature/flagd#790. Related to open-feature/flagd#990.

There is some trouble with circular-ish dependencies though. This needs to be merged for the integration test in open-feature/flagd#990 to pass, but this needs open-feature/flagd#990 to be merged to compile. I tested locally with a replace statement and everything was fine.

This PR also cleans up imports and moves to go.uber.org/mock from github.com/golang/mock which is no longer maintained.

[Kavindu-Dodan]

I released upstream flagd. However, we need to perform two more steps before acepting this

1. Fix releases propsed through this PR - fix: fix flagd dependencies #380
2. Release flagd testing and adopt latest flagd core release and testing release

Then we will not have the test failure caused by multiple protobuf registrations

[Kavindu-Dodan]

I have to block this till #372 (comment) is done. Otherwise thank you for taking care of this @craigpastro 🤝

[toddbaert]

@Kavindu-Dodan I did what you described here and tests are now passing. (I also had to update the go version in the CI to 1.20 (1.19 is deprecated now) to fix a compilation issue. I think we may want to update all go.mods to use v1.20, but lets do that in a separate PR.

[Kavindu-Dodan]

@Kavindu-Dodan I did what you described here and tests are now passing. (I also had to update the go version in the CI to 1.20 (1.19 is deprecated now) to fix a compilation issue. I think we may want to update all go.mods to use v1.20, but lets do that in a separate PR.

Awesome, thanks for taking care of the dependency bump 🤝

[Kavindu-Dodan]

LGTM 🎉

[Kavindu-Dodan]

@craigpastro thank you again for the contribution :)

[craigpastro]

My pleasure!