Description of proposed changes

This PR makes four changes to the GMT documentation:

1. Add a GMT Team page that contains a Distinguished Contributors section which can be used to recognize people's efforts. This is largely based on the project Jupyter distinguished contributors model and the NumPy team page. Suggestions are welcome for the recognition model, in which new distinguished contributors are decided upon by the people listed on the page annually.
2. Change AUTHORS.md to THANKS.md to better reflect the updated contents.
3. Move pages that are in the Developer Resources toctree to the devdocs folder and updates links accordingly.
4. Rename Developer Documentation page to GMT Enhancement Proposals to provide more descriptive information about the contents.

If this is approved, we should change the redirect for https://www.generic-mapping-tools.org/team from https://github.com/GenericMappingTools/gmt/blob/master/AUTHORS.md.

Fixes #2330
Fixes #5567

Reminders

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