📖 docs: add pre-release actions to release guide

[salasberryfin]

What this PR does / why we need it:

Add a post-release actions section to release guide.

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

Checklist:

• squashed commits into logical changes
• includes documentation
• adds unit tests
• adds or updates e2e tests

[salasberryfin]

My proposal is to have it documented for now and think about a potential automation in parallel. I updated the docs to reflect that E2E must be updated, as suggested by @furkatgofurov7

[salasberryfin]

Thanks @furkatgofurov7 for suggesting we follow a similar release procedure to the one in upstream CAPI https://github.com/kubernetes-sigs/cluster-api/blob/main/docs/release/release-tasks.md#prepare-main-branch-for-development-of-the-new-release. I'll update the docs and align the actions with this workflow.

[furkatgofurov7]

@salasberryfin let's fix some small notes and re-run e2e tests on this one, once you are back 😉

[furkatgofurov7]

@salasberryfin would you have time to update this PR soon?

[salasberryfin]

Thanks for the reminder @furkatgofurov7. I forgot that this was still open.

[Danil-Grigorev]

Thanks!