Adds one or more tags to an existing support request. The operation is surgical — only the tags listed in the request are added; existing tags on the ticket are preserved. Re-adding a tag that is already present is a successful no-op.

All submitted tags are normalized (trim + lowercase) before storage. For customers, the system additionally applies a customer_tag/ namespace prefix to prevent collisions with internal DoiT process tags. The response echoes the actual stored strings so callers can verify the transform.