Add to-announce to FCPs once they are finished

[spastorino]

We would need to automatically add a to-announce label to finished FCPs on rust repo, so our prioritization cli can pick them up to make the announcements of them. Otherwise we would get this full list of finished FCPs.

[LeSeulArtichaut]

There is no to-announce label in the rust-lang/rust repo. Once we’ve created it, we should be able to use triagebot’s autolabeling system to add it whenever the finished-final-comment-period label is added.

[spastorino]

@LeSeulArtichaut yeah I know, adding the label would be step 1 :). Going to ask Niko and/or Felix about this.

[spastorino]

@LeSeulArtichaut I've talked to Niko, we agreed on this and just created the label.

[LeSeulArtichaut]

@spastorino Should we add it on all finished FCPs or only on T-compiler ones?

[spastorino]

If they are properly tagged I'd say only T-compiler ones.

[spastorino]

I've implemented this in triagebot and rfcbot.

rust-lang/triagebot#762
rust-lang/rfcbot-rs#289