Add CTC check prior to tag promotion

[joshwlewis]

This adds a CTC check prior to promoting to main tags e.g. from heroku/heroku:24.v133 to heroku/heroku:24. This should prevent releases during deployment moratoriums.

GUS-W-16376259.

[edmorley]

@joshwlewis This check currently won't actually block releases, since CTC uses non-HTTP-200 responses to denote blocking a lock (https://github.com/heroku/tps/blob/master/docs/ctc.md#responses), and Curl ignores these unless the --fail argument is used.

eg compare to the Cheverny implementation, which checks for HTTP 200/201:
https://github.com/heroku/cheverny/blob/f27b132b8b829b16d2161977f00316faf0f06520/lib/mediators/stack/ctc_checker.rb#L27

For bonus points, we should probably also use --fail-with-body rather than --fail, since the former will also print the API response message:
https://curl.se/docs/manpage.html#--fail-with-body

[edmorley]

For even more bonus points, perhaps we should also add --connect-timeout and --retry to reduce flakiness?