DOC: Support dynamic filtering by tags for gallery examples with Sphinx-Gallery v0.21.0

[seisman]

Sphinx-Gallery v0.21.0 introduces tag support for gallery examples, which allows examples to be tagged and filtered more effectively. See https://sphinx-gallery.github.io/stable/configuration.html#tagging-examples-and-filtering for the usage and https://sphinx-gallery.github.io/stable/auto_examples/index.html?#general-examples for a live demo.

This feature would be very beneficial for the PyGMT gallery, which has grown substantially and can be difficult to navigate, especially for new users. Tag support would allow:

• Better discoverability of examples
• More flexible navigation
• Easier onboarding for new users
• Improved documentation structure without major reorganization

Potential checklist

• Decide if we want to support tags
• Decide on the list of allowed tags for PyGMT
• Document the list of allowed tags
• Upgrade to Sphinx-Gallery ≥ 0.21.0
• Add tags to gallery examples using the new tagging mechanism [definitely in multiple PRs]
• See if we should reorganize the structure of the gallery
• Update contributing guides

[Chuan1937]

Sure, we should add tags. Such as:

Tag	Description
maps	Maps and map elements
lines	Lines and curves
symbols	Symbols and markers
images	Images and grids
3d	3D plots
seismology	Seismology
basemaps	Basemaps (dual y-axis, ternary, etc.)
histograms	Histograms and rose diagrams
embellishments	Embellishments (colorbars, legends, etc.)
projections	Map projections
beginner	Beginner-friendly
advanced	Advanced