Migrate to proto api v2

[ilaleksin]

This PR addresses upgrade from github.com/golang/protobuf to google.golang.org/protobuf/proto

Changes:

• generate file descriptors of dependecies with v2 protoreflect API
• empty message v1 -> empty message v2
• significant update end-two-end-grpc-gateway example. It doesn't affect the logic, the example still works locally (i.e. steps from README return extected responses)

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[LorenzHW]

@ilaleksin thanks for the contribution. Can you make sure that the test suite ran once as part of this PR. The GitHub action should have been triggered as in this PR and results should be green.

Maybe we need to adapt the Github action to have:

  pull_request:
    branches:
      - main

[LorenzHW]

@fideltak hmm weird. Still not triggering. You ran tests locally I assume? Will take a look at the PR in the upcoming days.

[ilaleksin]

Hey @LorenzHW,
Unit tests for this PR will run after approval from a maintainer.

Could you launch the workflow?

[LorenzHW]

Alright, thanks @ilaleksin. I am sorry, I am so swamped with life right now, that I haven't found the time to review :(