augur curate format-dates

[joverlee521]

Context

Augur commands expect dates to be in ISO 8601 format so we should provide a robust way for users to convert any date format to ISO 8601. We've used many ways to tackle this date formatting issue throughout the Nextstrain ecosystem:

• using manual annotations in fauna.vdb.upload
• using pandas date parser in augur.parse.fix_dates
• using Python datetime module in ncov-ingest/transform
• using Python datetime module in monkeypox/ingest

See #860 for more details of the general augur curate design/structure.

Description

augur curate format-dates should adopt the latest iteration of robust date formatting from monkeypox/ingest. We should keep masking incomplete dates with XX as the default behavior since this is expected in other Augur commands. However, we should probably provide a flag to allow users to skip masking if desired.

There various other improvements that can be added as well:

• catch escaped directives edge cases (see monkeypox/ingest post-merge review comment)
• improve readability by explicitly listing directive combinations (see monkeypox/ingest post-merge review comment)
• add support for platform-specific directives (see monkepox/ingest post-merge review comment)