feature: write run duration into `auto_build_succeeded_comment`

[matthiaskrgr]

something like ☀️ Test successful after 3hours 21 minutes would useful from time to time.

[Kobzol]

Blocked on #487.

[bncer]

Sorry for the long delay. I'm currently doing duration part.

[Kobzol]

#487 has been merged, so this is now unblocked :)

[reddevilmidzy]

@rustbot claim

[rustbot]

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