Document maintainer actions (#6386)

## Which problem is this PR solving?

Fixes #6370 

## Description of the changes
Adding a section in the document on onboarding, offboarding and other
activities.

## Checklist
- [X] I have read
https://github.com/jaegertracing/jaeger/blob/master/CONTRIBUTING_GUIDELINES.md
- [X] I have signed all commits

---------

Signed-off-by: Jonah Kowall <[email protected]>
Signed-off-by: Yuri Shkuro <[email protected]>
Co-authored-by: Yuri Shkuro <[email protected]>

MAINTAINERS.md

@@ -22,3 +22,25 @@ We are grateful to our former maintainers for their contributions to the Jaeger
 * [@objectiser](https://github.com/objectiser)
 * [@tiffon](https://github.com/tiffon)
 * [@vprithvi](https://github.com/vprithvi)
+
+### Maintainer Onboarding
+
+Upon approval, the following steps should be taken to onboard the new maintainer:
+
+*   **1. Update Project Documentation**
+    *   **`MAINTAINERS.md` File:** Merge the PR to add the new maintainer to the `MAINTAINERS.md` file(s) in the relevant Jaeger repositories.
+*   **2. Grant Permissions**
+    *   **GitHub:** Add the new maintainer to the `@jaegertracing/jaeger-maintainers` GitHub team. This grants them write access to the Jaeger repositories.
+    *   **CNCF Mailing List:** Add the new maintainer to the `[email protected]` mailing list (and any other relevant Jaeger mailing lists). Contact the existing `cncf-jaeger-maintainers` to find out the precise process for adding to the mailing list, it will likely involve getting in touch with the CNCF.
+    *   **CNCF Maintainer Registry:**
+        *   Create a PR against the `cncf/foundation` repository to add the new maintainer's information to the `project-maintainers.csv` file. The following fields are required:
+        *   Reference the PR in the `cncf-jaeger-maintainers` mailing list.
+    *   **Signing Keys:**
+        *   Jaeger uses a GPG key for encrypted emails sent to the maintainers for security reports along with access to the `maintainers-only` GitHub repository. This key is stored in our 1password repository. 
+    *   **1Password:** Connect with an existing maintainer to be added to our jaegertracing 1Password team.
+*   **3. Announcement**
+    *   Announce the new maintainer to the Jaeger community through the mailing list, blog, or other appropriate channels.
+
+### Maintainer Offboarding
+
+The process for removing a maintainer is similar to adding one. A maintainer can step down voluntarily or be removed by a vote of the other maintainers if they are no longer fulfilling their responsibilities or are violating the project's Code of Conduct. A supermajority vote is needed to remove a maintainer. Their access should be revoked from all relevant tools, and the project documentation updated accordingly.