PGO: Move to a simpler process to merge the profiles

# Description

With the introduction of PGO in https://github.com/elastic/apm-server/pull/13884, we are relying on multistep process to collect, preserve and update CPU profile via automated pull requests raised by the benchmarks workflow. However, the pull request process might be unnecessary in the long run since it requires manual steps to review and approve each PR separately. Ideally, after some grace period we move towards a simpler process where updated CPU profile is merged directly into the main branch without raising a pull request at all.