add custom s3 support storage config option (#239)

Options are documented here including an example
on how to set a custom endpoint:

https://guides.rubyonrails.org/active_storage_overview.html#s3-service-amazon-s3-and-s3-compatible-apis

.env.example

@@ -107,3 +107,12 @@ BRAND_NAME=
 # CLOUDFLARE_SECRET_ACCESS_KEY=
 # CLOUDFLARE_BUCKET=
 #
+# Generic S3
+# ==========
+# ACTIVE_STORAGE_SERVICE=generic_s3 <- Enables Generic S3 storage
+# GENERIC_S3_ACCESS_KEY_ID=
+# GENERIC_S3_SECRET_ACCESS_KEY=
+# GENERIC_S3_REGION=
+# GENERIC_S3_BUCKET=
+# GENERIC_S3_ENDPOINT=
+# GENERIC_S3_FORCE_PATH_STYLE= <- defaults to false