Rename master branch to main

[ashb]

Once 2.0.0 is out and fully released, we should switch over from master to main as our default branch, deleting/renaming master.

Rough steps:

• Check if the ASF GitBox sync needs to know about this
• Update all CI pipelines that check for master Prepare to rename master branch for main. #14688
• Rebase all PRs with an INFRA ticket
• Update all docs

Thankfully GitHub as done a lot of work to make this transition easier https://github.com/github/renaming/ - we may want to wait for the "auto rename" feature GitHub promised here, or maybe we just do it anyway.

[potiuk]

Absolutely!

[turbaszek]

You need to fill issue to Apache Infra and that all PRs have to change the base branch. We did this in Apache Kibble:
https://github.com/apache/kibble/issues/45

[mik-laj]

Similar: #9351

[ashb]

Done.