[ENH] Allow LICENSE files to have .txt, .md, or .rst extensions

[monique2208]

Allow extension for the LICENSE file: #2021

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.45%. Comparing base (a2a491d) to head (3eaa005).
Report is 10 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2036   +/-   ##
=======================================
  Coverage   82.45%   82.45%           
=======================================
  Files          17       17           
  Lines        1499     1499           
=======================================
  Hits         1236     1236           
  Misses        263      263           

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[effigies]

Please also update:

bids-specification/src/modality-agnostic-files.md

Lines 5 to 11 in f0e14a2

	Templates:
	- `dataset_description.json`
	- `README[.md|.rst|.txt]`
	- `CITATION.cff`
	- `CHANGES`
	- `LICENSE`

bids-specification/src/schema/objects/files.yaml

Lines 23 to 48 in f0e14a2

	LICENSE:
	display_name: License
	file_type: regular
	description: |
	A `LICENSE` file MAY be provided in addition to the short specification of the
	used license in the `dataset_description.json` `"License"` field.
	The `"License"` field and `LICENSE` file MUST correspond.
	The `LICENSE` file MUST be either in ASCII or UTF-8 encoding.
	README:
	display_name: README
	file_type: regular
	description: |
	A REQUIRED text file, `README`, SHOULD describe the dataset in more detail.
	The `README` file MUST be either in ASCII or UTF-8 encoding and MAY have one of the extensions:
	`.md` ([Markdown](https://www.markdownguide.org/)),
	`.rst` ([reStructuredText](https://docutils.sourceforge.io/rst.html)),
	or `.txt`.
	A BIDS dataset MUST NOT contain more than one `README` file (with or without extension)
	at its root directory.
	BIDS does not make any recommendations with regards to the
	[Markdown flavor](https://www.markdownguide.org/extended-syntax/#lightweight-markup-languages)
	and does not validate the syntax of Markdown and reStructuredText.
	The `README` file SHOULD be structured such that its contents can be easily understood
	even if the used format is not rendered.
	A guideline for creating a good `README` file can be found in the
	[bids-starter-kit](https://github.com/bids-standard/bids-starter-kit/tree/main/templates/).

[effigies]

LGTM. Thanks!

[effigies]

@monique2208 Thanks! Be sure to add yourself to https://github.com/bids-standard/bids-specification/wiki/Recent-Contributors!