Add directory fallback behavior

[benalleng]

This adds the ability for a backup directory to be chosen by the receiver incase of a failure on the ohttp key fetch.

As well now that there is Relay and directory management the Struct is better suited as MailroomManager.

Supersedes #1294

relates to the directory fallbacks in #1007

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[coveralls]

Coverage Report for CI Build 28387717154

Coverage decreased (-0.002%) to 85.515%

Details

• Coverage decreased (-0.002%) from the base build.
• Patch coverage: 16 uncovered changes across 2 files (36 of 52 lines covered, 69.23%).
• 1 coverage regression across 1 file.

Uncovered Changes

File	Changed	Covered	%
payjoin-cli/src/app/v2/ohttp.rs	37	22	59.46%
payjoin-cli/src/app/v2/mod.rs	2	1	50.0%
Total (3 files)	52	36	69.23%

Coverage Regressions

1 previously-covered line in 1 file lost coverage.

File	Lines Losing Coverage	Coverage
payjoin-cli/src/app/config.rs	1	81.01%

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Coverage Stats

Relevant Lines:	15161
Covered Lines:	12965
Line Coverage:	85.52%
Coverage Strength:	361.12 hits per line

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💛 - Coveralls