Add pameeela to MAINTAINERS.txt as a provisional committer team facilitator

Problem/Motivation

In #2974016: Add "committer team facilitator" and "core initiative facilitator" roles to core governance, we've adopted a proposal that adds two new facilitation roles to core governance.

@pameeela is already actively performing the role of a provisional committer team facilitator, but this is not Syet reflected in MAINTAINERS.txt. She also should have permissions to maintain issues in her role (e.g., to reopen an issue that's missing a release note or such), but doesn't yet have permissions to do that since she was never formally added as a maintainer.

Proposed resolution

Patch MAINTAINERS.txt to add Pam, and grant her "maintain issues" permissions on the core project.

Remaining tasks

• A comment from Pam that she's comfortable with provisional maintainership as described in #2974016: Add "committer team facilitator" and "core initiative facilitator" roles to core governance.
• Dries needs to sign off on the patch.
• Add permissions as per: https://www.drupal.org/core/maintainers/provisional-committers (@xjm has added "maintain issues" permission in advance to help facilitate the 8.8.0-alpha1 release notes process.)
• Followup needed: Actually patch the core governance with the role definition from #2974016: Add "committer team facilitator" and "core initiative facilitator" roles to core governance.