Send event stream start events

[rvolosatovs]

Summary

References #2950

Changes

• Reintroduce events.stream.start

Testing

Ran console

Regressions

Console-related

Notes for Reviewers

Please DO NOT depend on events.stream.start - console must completely ignore this event, the only purpose of it is to ensure that headers are sent.
As part of #2950 I will later investigate how we could fix this without relying on such workarounds. ( hence, also, the issue is not closed, but merely referenced)
Assigning @johanstokking since I'm almost done for today and off tomorrow

@kschiffer these entries should not be present:

Checklist

• Scope: The referenced issue is addressed, there are no unrelated changes.
• Compatibility: The changes are backwards compatible with existing API, storage, configuration and CLI, according to the compatibility commitments in README.md for the chosen target branch.
• Documentation: Relevant documentation is added or updated.
• Changelog: Significant features, behavior changes, deprecations and fixes are added to CHANGELOG.md.
• Commits: Commit messages follow guidelines in CONTRIBUTING.md, there are no fixup commits left.

[htdvisser]

LGTM. Please remove the line "Event stream start and stop events are not published anymore." from CHANGELOG instead of adding a line that they are sent.

[johanstokking]

I removed the change from the changelog as it's effectively reverted when it's not released yet