[PROPOSAL] Document running campaigns

[dblock]

What/Why

What are you proposing?

We have a concept of campaigns, e.g. campaigns in opensearch-build. Document how those are created/run.

AFAIK that is:

1. Identify a repo where to run a campaign (e.g. opensearch-clients for all clients, or opensearch-plugins for all plugins).
2. Create a parent issue in that repo.
3. Use meta to create child issues in all related repos, linking back to the parent issue by saying "Coming from ..."
4. Create manual issues in any remaining repos, e.g. OpenSearch for when wanting a change in all plugins and OpenSearch.
5. Update the parent issue with - [ ] link to each child GH issue, now each child will say "tracked in parent"
6. Label all issues for a release.

What users have asked for this feature?

Coming from opensearch-project/opensearch-plugins#163 (comment)

What problems are you trying to solve?

Create a standard procedure for making campaigns.