Fix metrics spawn in serve_acme

[spacebear21]

In my rebase I forgot to spawn the metrics server in serve_acme.

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[coveralls]

Pull Request Test Coverage Report for Build 21720901000

Details

• 0 of 3 (0.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.01%) to 83.263%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
payjoin-service/src/lib.rs	0	3	0.0%

Totals
Change from base Build 21720184564:	-0.01%
Covered Lines:	10238
Relevant Lines:	12296

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💛 - Coveralls

[benalleng]

ACK a9510b5