[chore] Add Dependabot auto-update-workflow

[julianocosta89]

Changes

This PR adds a new workflow to allow Dependabot to auto update the generated proto files when the google.golang.org/grpc/cmd/protoc-gen-go-grpc package is bumped.

This will avoid manual tasks like we had to do in:

• build(deps): bump the go-production-dependencies group across 2 directories with 6 updates #1807
• build(deps): bump the go-production-dependencies group across 2 directories with 16 updates #1802

Merge Requirements

For new features contributions, please make sure you have completed the following
essential items:

• [ ] CHANGELOG.md updated to document new feature additions
• [ ] Appropriate documentation updates in the docs
• [ ] Appropriate Helm chart updates in the helm-charts

[julianocosta89]

@CharlieTLe would you be able to take a look?

Basically created the token with the permissions you have shared in #1802 and copied your workflow: https://github.com/CharlieTLe/opentelemetry-demo/blob/6a07a6e29a18c3d8dfe89e7596054f06439f6504/.github/workflows/dependabot-auto-update-protobuf-diff.yml

Only one thing I didn't quite get.

Is this hash coming from somewhere?
git config user.email "49699333+dependabot[bot]@users.noreply.github.com"

Should I adapt it here?

[CharlieTLe]

Yeah, it should be adapted here. I got it from looking at the email on commit it makes.

For example, on https://github.com/open-telemetry/opentelemetry-demo/commit/40ff491f719137e37207e66aa03166438c843f8a.patch, we can see the line:

From: "dependabot[bot]" <49699333+dependabot[bot]@users.noreply.github.com>

I picked this username so that if we ask dependabot to do a rebase, it doesn't complain that someone else besides it did the commit.