v2.0: ledger-tool: Fix create-snapshot default value for output_directory (backport of #3148)

[mergify]

Problem

The arguments to specify full and incremental snapshot archives paths used to be a global argument; these were moved to only be instantiated on commands that needed them in #1773.

But, when the arguments were moved from app-level to subcommand-level, the code that matches the arguments was not updated to look at subcommand-matches instead of app-matches.

Summary of Changes

Examine the correct matches

Fixes #3117

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This is an automatic backport of pull request #3148 done by Mergify.

[steviez]

My case for BP'ing this is that:

• There restores behavior that was unintentionally broken
• The change is very limited, only effects ledger-tool / no downstream deps

[brooksprumo]

[t-nelson]

did we varify that this doesn't lose visibility of global args? i vaguely remember fighting this at one point

[steviez]

did we varify that this doesn't lose visibility of global args? i vaguely remember fighting this at one point

Sorry, not sure I follow the question. These two args are now intentionally subcommand args (ie agave-ledger-tool --help will not show them, whereas agave-ledger-tool create-snapshot will), so we need to be matching the subcommand (arg_matches) instead of global (matches). Switching from global to subcommand (as this PR does) for these two args does not affect any other args

[t-nelson]

i have seen arg_matches not contain entries that matches does contain for the same invocation