chore: auto-label T-shirt size indicator should be assigned on every new pull request in all googleapis repositories

[losalex]

Can we enable Size Label Bot on all googleapis repositories? Below some data points:

1. It runs already pretty flawless on google-cloud-go, nodejs-logging, java-logging, python-logging and 6 more.
2. It runs only when PR is modified and does not runs on scheduler events, so the bot should not consume too much resources.
3. It will make sure that size indicator exists on every PR same as it is done in rest of company systems.

[jskeet]

For google-cloud-dotnet, I'd be nervous of it generating even more emails per OwlBot PR - especially as the size will almost always change between the initial OwlBot generation and the subsequent post-processing. Maybe the label doesn't generate an email, which wouldn't make it too bad. There's still quite a lot happening on even the most trivial PRs though - example. It can become slightly tricky to see the really important bits with lots of bots weighing in on every PR.

That said, I'm happy to try it...

[losalex]

For google-cloud-dotnet, I'd be nervous of it generating even more emails per OwlBot PR - especially as the size will almost always change between the initial OwlBot generation and the subsequent post-processing. Maybe the label doesn't generate an email, which wouldn't make it too bad. There's still quite a lot happening on even the most trivial PRs though - example. It can become slightly tricky to see the really important bits with lots of bots weighing in on every PR.

That said, I'm happy to try it...

Thank you @jskeet for sharing your concern and willingness to try it! Currently Size-Label bot is enabled on 11 repositories and based on my observation I have not seen extra emails as a result of this bot activity. Worth mentioning that this bot is smart enough not to update same label in case if PR size was not changed.

[losalex]

As decided, Size-Label bot is going to be enabled on several googleapi repositories per language - below are associated PRs: 1384, 1383, 1382, 1381