Update releases to refer to month instead of two weeks

[grabbou]

We also have to update internal guides.

CC: @mkonicek

[facebook-github-bot]

By analyzing the blame information on this pull request, we identified @satya164 to be a potential reviewer.

[satya164]

@facebook-github-bot shipit

[mkonicek]

@grabbou @satya164 1st of January might be ambitious given it's the New Year's Day? :)

In general hitting the exact date every month might be difficult. How about saying "within first few days of each month"?

[mkonicek]

@satya164 Not sure why the bot didn't work :/

[mkonicek]

This landed internally but exporting back to GitHub failed.

[fredemmott]

It got exported to github: 830d7f6

• the bot message didn't appear here for some unknown reason
• the 'Closes Update releases to refer to month instead of two weeks #11269' part was removed because 'CC:' is magic to our internal tools

Closing because this PR has been merged, github just doesn't know.