Standardize branching to match OpenSearch

[dblock]

Coming from .github#13, standardize release branching to match what OpenSearch is doing.

1. Create a 1.0 branch for the OpenSearch 1.0 release, 1.x branch for next 1.1 release, and use main for 2.0 development. Make sure CI is enabled on those.
2. Update your release/branching documentation. If you don't have one, add a RELEASING.md that links to, or has content from .github/RELEASING.md.
3. If you are using a develop branch, stop. You should be using the default main brach for furthermost, future development.
4. Delete any merged/stale/develop/feature branches that are no longer in use.
5. Communicate any changes in process to your team.

Refer to release branching for more information.

[eirsep]

@Bukhtawar can you take this up? I don't have permission to delete branches.

https://github.com/opensearch-project/asynchronous-search/branches

[eirsep]

@CEHENKLE We don't have permissions to delete branches on the repo. Can you please help with the deletion. Post that we can assign ourselves to this issue and take it forward

[CEHENKLE]

@eirsep sure. Do you want to 1/ tell me explicitly what branches you want to delete, and I'll do it. 2/ make the change in the branch protection rule to allow deletion of branches (and you can do it)?

[Bukhtawar]

I'd prefer 2 we need to protect main and all version branches only

[CEHENKLE]

Branch deletion should be enabled now.