[CVC Storage] Add interactions to CVC save prompt for server cards

When CVC is detected for an existing server card during checkout, the
users are offered a prompt to save the CVC.

Add user interactions to the Message.

Note: The metrics will be added in a follow-up change.

Bug: 1485194
Change-Id: I04db3b03f8b47db42a3ba0bf547786e1fe0e8513
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4906641
Reviewed-by: Jan Keitel <jkeitel@google.com>
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Commit-Queue: Vishwas Uppoor <vishwasuppoor@google.com>
Reviewed-by: Florian Leimgruber <fleimgruber@google.com>
Cr-Commit-Position: refs/heads/main@{#1209279}