change(doc): Update README and release checklist for the release candidate

[teor2345]

Motivation

We want to change how we tag and release the release candidate.

Dependencies

The README and release checklist Docker instructions won't work until we fix:

• fix(docker): Add edge tag to Docker images, document when latest tag will appear #5312
• fix(docker): Make default command work in docker images, disable optional listener ports #5313

Solution

• Update the README for the release candidate
  • Update goals
  • Add a docker run command
• Update the release template for the release candidate
  • Update process to match what we currently do
  • Use the docker run command from the README for testing

Fix #4953
Fix #4954

Review

I think Pili wanted to review this, but other engineers might want to as well.

Reviewer Checklist

• Will the PR name make sense to users?
  • Does it need extra CHANGELOG info? (new features, breaking changes, large changes)
• Are the PR labels correct?
• Does the code do what the ticket and PR says?
• How do you know it works? Does it have tests?

Follow Up Work

[mpguerra]

Looks good overall, I think we may need to finalise some details before we can publish though

[mpguerra]

LGTM

[gustavovalverde]

LGTM