Catch exceptions and show error when save template to repo fails.

Fixes [#80215916]

This PR augments the API PR (https://github.com/CenturyLinkLabs/panamax-api/pull/218), to catch the exception raised by `save_template_to_repo`, and displays an error message to the user. Catching the exception here keeps the user on the Save as Template screen, and provides an appropriate context to the error message.