Require Maintainers to be Triagers

The project is looking for ways to improve community relationships, and
one of the suggestions is to require maintainers to share triager
responsibilities to provide timely and useful feedback to contributors
on their issues and pull requests.

The proposal is to assume privileges and responsibilities and membership
is monotonically expanding so that:

- all triagers are members (already the case);
- all maintainers are triagers (this proposal).

Or if these were python sets, then... ;)

```
Contributor <= Member <= Triager <= Maintainer
```

Context: we are considering automatic assignment of a number of Triagers
to every new pull request, and it's important that this burden is shared
by all seasoned members, incl. maintainers.

Note: once this is approved, someone should walk through the list of
current Maintainers and add them to Triagers groups for appropriate
repos. Alternatively, Maintainers groups can be converted into nested
groups, see:

https://docs.github.com/en/organizations/organizing-members-into-teams/about-teams#nested-teams

Signed-off-by: Ihar Hrachyshka <[email protected]>

Author: booxter

CONTRIBUTOR_ROLES.md

@@ -115,9 +115,13 @@ Maintainers will vote publicly on the issue, expressing their support via a GitH
 
 After a [decision has been made](https://github.com/instructlab/community/blob/main/governance.md#decision-making-at-the-instructlab-org-level), a Maintainer will create a PR to add you in the [MAINTAINER file](https://github.com/instructlab/community/blob/main/MAINTAINERS.md) within three weeks.
 
+All Maintainers are Triagers. If a candidate is not a Triager at the time of the nomination, they should be added to both Triagers and Maintainers teams.
+
 #### Maintainer responsibilities and Privileges
 
-As a project Maintainer, you have the following responsibilities and privileges:
+All Maintainers are Triagers and share all of the appropriate [responsibilities and privileges](#triager-responsibilities-and-privileges).
+
+In addition, as a project Maintainer, you have the following responsibilities and privileges:
 
 * You make and approve technical design decisions.
 * You set technical direction and priorities.