Add warnings to summary if migrations have issues (timing, etc)

Currently the bot just reports a list of information about the migrations. But it would be more helpful for people if we called out migrations that are expected to take a long time or failed.

Definition of Done

• There is a Warnings section at the top of the merge request comment
• Warning section should list migrations that don't comply with standard timings
• If the migration by itself needs communication with SRE, we should call that out

/cc @ali-gitlab @craig-gomes @abrandl