feat(mastodon): Add own helm chart to repository

This patch introduces an own helm chart, which is basically a
copy of the upstream chart, but with adjustments made to it, to
fit with my current style of deployment.

Given the current uncontrolled nature of adjustments to the
upstream chart, it might cause unexpected outages and alike,
moving this chart into my own repository should prevent that
and allow to use the standard flow.

Further not all my changes are upstream yet and might never be,
given that many people are working on the same problems right
now.

Refrences:
https://github.com/mastodon/mastodon/pull/20733