Add Helm chart (#14090)

* 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

chart/templates/secrets.yaml

@@ -0,0 +1,28 @@
+apiVersion: v1
+kind: Secret
+metadata:
+  name: {{ template "mastodon.fullname" . }}
+  labels:
+    {{- include "mastodon.labels" . | nindent 4 }}
+type: Opaque
+data:
+  {{- if not (empty .Values.secrets.secret_key_base) }}
+  SECRET_KEY_BASE: "{{ .Values.secrets.secret_key_base | b64enc }}"
+  {{- else }}
+  SECRET_KEY_BASE: {{ required "secret_key_base is required" .Values.secrets.secret_key_base }}
+  {{- end }}
+  {{- if not (empty .Values.secrets.otp_secret) }}
+  OTP_SECRET: "{{ .Values.secrets.otp_secret | b64enc }}"
+  {{- else }}
+  OTP_SECRET: {{ required "otp_secret is required" .Values.secrets.otp_secret }}
+  {{- end }}
+  {{- if not (empty .Values.secrets.vapid.private_key) }}
+  VAPID_PRIVATE_KEY: "{{ .Values.secrets.vapid.private_key | b64enc }}"
+  {{- else }}
+  VAPID_PRIVATE_KEY: {{ required "vapid.private_key is required" .Values.secrets.vapid.private_key }}
+  {{- end }}
+  {{- if not (empty .Values.secrets.vapid.public_key) }}
+  VAPID_PUBLIC_KEY: "{{ .Values.secrets.vapid.public_key | b64enc }}"
+  {{- else }}
+  VAPID_PUBLIC_KEY: {{ required "vapid.public_key is required" .Values.secrets.vapid.public_key }}
+  {{- end }}