Changed process for releaser key updates in `docker-node`

Situation

The GOVERNANCE > Adding new releasers documentation section instructs a new releaser to:

Open a PR in nodejs/docker-node to add their GPG key to node.keys.

The process to maintain releasers keys in the nodejs/docker-node repo has been partially automated, so that manual PR creation by a new releaser (or for any other change in releaser keys) is no longer necessary.

If a PR is created, the @nodejs/releasers team is included as reviewers.

Suggestion

Since there is no longer any proactive manual action required in the nodejs/docker-node repo from releasers when keys change, the reference to manually opening a PR could be removed.

It could be replaced with a description to say that the keys are automatically checked once a week on Mondays.

cc: @nschonni

Start with the “Adding new releasers” section in GOVERNANCE.md and compare its instructions with the current automated process in nodejs/docker-node. Remove the manual PR instruction and document that releaser keys are checked automatically each Monday; confirm the rendered Markdown accurately reflects the updated process.