Add data directory to gitignore

[zealsham]

When you run the new payjoin-service, it creates a data directory which isn't part of the gitignore files and thus getting tracked by git.

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Pull Request Test Coverage Report for Build 21283264520

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• Overall coverage remained the same at 83.203%

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Totals
Change from base Build 21267453749:	0.0%
Covered Lines:	10140
Relevant Lines:	12187

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💛 - Coveralls

[DanGould]

this makes me question whether the data in the data directory is in the home it ought to be in

[zealsham]

this makes me question whether the data in the data directory is in the home it ought to be in

the current behaviour creates the data directory in whatever working directory the binary is called from. We should have a dedicated directory just as we have for the cli

[spacebear21]

The directory is configurable in config.toml and defaults to ./data. Arguably we could not set a default and require it to be explicit, as Yuval suggested here #1095 (comment)

FWIW I had added *.dat to the .gitignore in payjoin-service, I suppose that's not effective if the binary is run from the top-level directory, perhaps we should move that to this top-level .gitignore (I'd also prefer using specific known files instead of a common dir name like data in .gitignore).

[DanGould]

specific file > common directory name. Agree cACK