mastodon: Add Helm values; move to chart 6.10.6 (Mastodon 4.7.5).

Upgraded 4.5.21 -> 4.6.11 -> 4.7.5 with the chart's migration hooks.
Secrets live in unmanaged Secrets (mastodon-app*); the OIDC client
secret is in the untracked values-secrets.yaml.  Bitnami's free images
moved to bitnamilegacy, including the ES volume-permissions image.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Change-Id: I74df14f38b76a3a5d1e93f21380d8c65a5de6665
2 files changed