Docs: Contributing strategy and how to backport changes

[acarbonetto]

Describe the feature

From: #2411

We now contribute to release branch, and need a strategy to enforce backport changes.

Use Case

All release changes

Proposed Solution

Suggestions:

• individual contributors should backport changes as part of their issue, OR
• reminder to individual contributors backport changes once PR is merged, OR
• setup a backport manager to automatically create PRs from release-1.2 to main, and from release-1.1 to release-1.2 and main.

Other Information

No response

Acknowledgements

• I may be able to implement this feature request
• This feature might incur a breaking change

Client version used

N/A

Environment details (OS name and version, etc.)

N/A