* 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
