- move application variables under `mastodon` namespace
- restore standard yaml structure for ingress configuration
- move values.yaml.template to values.yaml

* add Helm chart

known issues/future work:

- SSO is unsupported

- S3/Minio/GCS is unsupported

- Swift is unsupported

- WEB_DOMAIN is unsupported

- Tor is unsupported

* helm: clarify how LOCAL_DOMAIN is set

* helm: add chart description

* helm: make DB_POOL and Sidekiq concurrency configurable

* helm: only enforce pod affinity when using ReadWriteOnce

* helm: clarify compatibility

* helm: clean up application variables

* helm: add job to create initial admin