Sanitize taskcluster_scope_prefixes

[mitchhentges]

See previous discussion. TL;DR: Rather than leaving this config flexible and letting workers drift, encode a specific format that we care about

• Check if this sort of validation is relevant to all scriptworker scripts. If yes, find more-general target for this solution than just pushapkscript
• Validate taskcluster_scope_prefixes so that it expects a terminating :. If it fails validation, stop pushapkscript immediately with a message explaining why

[lundjordan]

@mitchhentges how important is this? Should we track it on the pipeline board?

[mitchhentges]

It depends on the minimum granularity of work that we want to put on the pipeline board: in our ideal +trello workflow, will there ever be any github tickets that we work on that aren't ported to Trello?

If yes, then this is a candidate of such a ticket. It's small, and it isn't an incredibly high priority - it'll ease the burden of maintenance, but not by several orders of magnitude.
However, if every ticket we work on should be ported to Trello, then yes, this should be tracked on the pipeline board as well, because it is still relevant work that needs to be done

[lundjordan]

discussed this more in slack. based on current criteria, I think this just fits in under backlog.

criteria for backlog
• be top priority after planned work is done or blocked
• directly improve reliability of CI and releases, reduce infra cost, or reduce human maintenance