[processor] Add experimental label to canary channel

[Hexcles]

Fixes #1635

This must land right after web-platform-tests/wpt#20240 .

[foolip]

Won’t this cause both Dev and Canary to get the label, so that a random one of them ends up on the front page? Should we change the query of the front page to use concrete channel labels to not have to pretend Edge Dev is not experimental?

[Hexcles]

Yeah that's a great point that I didn't realize... Thanks, @foolip !

Short of a customizable homepage, I'd still prefer to show Edge Dev instead of Edge Canary by default for better alignment with Chrome. We should change the default query to accommodate this.

[foolip]

Approved so that it can be merged and released when the time is right.

Labeling both as experimental and changing the default query would solve most of the problem, but there may be people who have queries against the experimental label that they expect to be a consistent set of configurations. Not sure how to deal with that really.

[Hexcles]

Dropping this in favour of #2081