Participant / Sample External IDs in parser

[illusional]

Add support for multiple participant and external IDs in the parsers, in two ways:

• Allow some subclass to provide an implementation for get_{participant/sample}_external_ids.
• Add an implementation here for the GenericMetadataParser.
• Switching matching participants / samples to look through ALL IDs.
• Add a docstring to better describe parameters.
• Fix a bug in update parent / root for nested samples.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 81.91489% with 17 lines in your changes missing coverage. Please review.

Project coverage is 80.43%. Comparing base (e2dd775) to head (c63f2c9).

Files	Patch %	Lines
metamist/parser/generic_metadata_parser.py	72.09%	12 Missing :warning:
metamist/parser/generic_parser.py	88.63%	5 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #849 +/- ## ========================================== - Coverage 80.49% 80.43% -0.07% ========================================== Files 172 172 Lines 14540 14579 +39 ========================================== + Hits 11704 11726 +22 - Misses 2836 2853 +17 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.