Allow templating to succeed if postgres deployment is enabled but a connection string is defined

Signed-off-by: Rhea Danzey <rdanzey@element.io>

helm/dendrite/templates/_helpers.tpl

@@ -2,13 +2,13 @@
 {{- if not .Values.signing_key.create -}}
 {{-  fail "You must create a signing key for configuration.signing_key. (see https://github.com/matrix-org/dendrite/blob/master/docs/INSTALL.md#server-key-generation)" -}}
 {{- end -}}
-{{- if not (or .Values.dendrite_config.global.database.host .Values.postgresql.enabled) -}}
+{{- if and (eq .Values.dendrite_config.global.database.connection_string "") (not (or .Values.dendrite_config.global.database.host .Values.postgresql.enabled)) -}}
 {{-  fail "Database server must be set." -}}
 {{- end -}}
-{{- if not (or .Values.dendrite_config.global.database.user .Values.postgresql.enabled) -}}
+{{- if and (eq .Values.dendrite_config.global.database.connection_string "") (not (or .Values.dendrite_config.global.database.user .Values.postgresql.enabled)) -}}
 {{-  fail "Database user must be set." -}}
 {{- end -}}
-{{- if not (or .Values.dendrite_config.global.database.password .Values.postgresql.enabled) -}}
+{{- if and (eq .Values.dendrite_config.global.database.connection_string "") (not .Values.dendrite_config.global.database.password) (not .Values.postgresql.enabled) -}}
 {{-  fail "Database password must be set." -}}
 {{- end -}}
 {{- end -}}