Propagate sub-config parsing error

[DanGould]

For example, if the [v2] field had a pj_directory config field defined, but the URL parsing failed, the error would be swallowed before this change.

This now propagates that error to the CLI.

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The error propagation still isn't perfect, and some config errors get swallowed without complete context, but this is progress.

[spacebear21]

tACK d17bf0d

Example error message before:

❯ cargo run -- receive 1
     Running `/Users/spacebear/Projects/rust-payjoin/target/debug/payjoin-cli receive 1`
Error: V2 configuration is required for BIP77 mode

After:

❯ cargo run -- receive 1
     Running `/Users/spacebear/Projects/rust-payjoin/target/debug/payjoin-cli receive 1`
Error: Valid V2 configuration is required for BIP77 mode: missing field `ohttp_relay`

[coveralls]

Pull Request Test Coverage Report for Build 13838915414

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 4 of 14 (28.57%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.06%) to 80.505%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
payjoin-cli/src/app/config.rs	4	14	28.57%

Totals
Change from base Build 13838537049:	-0.06%
Covered Lines:	4782
Relevant Lines:	5940

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💛 - Coveralls