Docs: Feedback for BYOC- document we don't support custom tags

[jason-da-redpanda]

Issue description

we currently don't support adding custom tags.(after creation) .
if customer creates tags after cluster creation it can cause reconciliation failures.. which generates incidents.

This is more for pre-reqs on each of the links for creating BYOC ... to have a line saying we do not support custom tags.

Updates to existing documentation

BYOC Page source

Link to Redpanda Slack conversation

#sev-4-inc-2106-iam-untagpolicy-is-not-allowed-2025-04-23

[jason-da-redpanda]

note i updated this to be...(based on feedback from Camilo )
we currently don't support adding custom tags.(after creation) .

but sounds like we do or GCP..

https://redpandadata.slack.com/archives/C08P7LF4D9B/p1745499079574169?thread_ts=1745498501.353679&cid=C08P7LF4D9B