Making Jessica Grebenschikov a maintainer for promtool in the Prometheus repository

[Julien Pivotto]

Hello Prometheans,

I'd like to welcome Jessica as new maintainer for promtool, in the
prometheus/prometheus repository. Jessica has started contributing to
the project with a LFX mentorship, and has continuously worked on the
rules backfilling since then.

We already have consensus on the prometheus-team mailing list, therefore
this email is the announcement to the community.

Welcome Jessica!

--
Julien Pivotto
@roidelapluie

[Jessica Grebenschikov]

Thank you Julien, I'm really excited!