Add experimental functionality for labelling PRs by their size #1623

Job	Run time
Rust analysis (ubuntu-latest, stable-v2.19.3)	1m 5s
Rust analysis (ubuntu-latest, linked)	1m 37s
Rust analysis (ubuntu-latest, default)	2m 1s
Rust analysis (ubuntu-latest, stable-v2.22.1)	2m 1s
Rust analysis (ubuntu-latest, nightly-latest)	1m 38s
	8m 22s

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