WIP: Intros / Tutorials / Gallery: Include folder in colormap name

[yvonnefroehlich]

Description of proposed changes

Include the folder (https://github.com/GenericMappingTools/gmt/tree/master/share/cpt) in the colormap name in the examples

• intros
• tutorials
• gallery
• src
• tests
• datasets
• technical references
• contributing guide

Fixes #4308

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[yvonnefroehlich]

How do we want to update the comments? For new users the leading folder could be unclear. Edit maybe we don not need the "by Fabio Crameri" each time?

Suggested change

	# Create a colorbar suitable for surface topography - oleron
	# Create a colorbar suitable for surface topography - oleron from the Scientific colour maps (SCM) by Fabio Crameri

[seisman]

I don't think we need to explain it each time, just changing oleron to SCM/oleron.

[seisman]

Still need to update following lines:

pygmt/src/grd2cpt.py:180:        a categorical color table, like ``cmap="categorical"``.
pygmt/src/makecpt.py:165:        a categorical color table, like ``cmap="categorical"``.
pygmt/tests/test_makecpt.py:149:    makecpt(cmap="categorical", categorical=True, series=[0, 6, 1])
doc/techref/justification_codes.md:108:fig.colorbar(cmap="buda", frame=0, position="jMC+w10c/2c+h")
doc/contributing.md:692:    fig_ref.grdimage("@earth_relief_01d_g", projection="W120/15c", cmap="geo")
doc/contributing.md:693:    fig_test.grdimage(grid, projection="W120/15c", cmap="geo")

Perhaps also update turbo to google/turbo in the following lines:

pygmt/datasets/mercury_relief.py:62:    ``cmap="@mercury_relief.cpt"``, otherwise GMT's default CPT (*turbo*) will be used.
pygmt/datasets/earth_age.py:50:    ``cmap="@earth_age.cpt"``, otherwise GMT's default CPT (*turbo*) will be used. If
pygmt/datasets/moon_relief.py:63:    ``cmap="@moon_relief.cpt"``, otherwise GMT's default CPT (*turbo*) will be used. If
pygmt/datasets/earth_mean_dynamic_topography.py:48:    ``cmap="@earth_mdt.cpt"``, otherwise GMT's default CPT (*turbo*) will be used. If
pygmt/datasets/pluto_relief.py:61:    ``cmap="@pluto_relief.cpt"``, otherwise GMT's default CPT (*turbo*) will be used. If
pygmt/datasets/earth_mean_sea_surface.py:50:    ``cmap="@earth_mss.cpt"``, otherwise GMT's default CPT (*turbo*) will be used. If
pygmt/datasets/mars_relief.py:63:    ``cmap="@mars_relief.cpt"``, otherwise GMT's default CPT (*turbo*) will be used. If
pygmt/datasets/venus_relief.py:50:    ``cmap="@venus_relief.cpt"``, otherwise GMT's default CPT (*turbo*) will be used. If
pygmt/datasets/earth_dist.py:50:    ``cmap="@earth_dist.cpt"``, otherwise GMT's default CPT (*turbo*) will be used. If
pygmt/datasets/earth_relief.py:70:    dataset-specific CPT when plotting the dataset, explicitly set ``cmap="geo"``,
pygmt/datasets/earth_deflection.py:58:    ``cmap="@earth_defl.cpt"``, otherwise GMT's default CPT (*turbo*) will be used. If
pygmt/datasets/earth_vertical_gravity_gradient.py:50:    ``cmap="@earth_vgg.cpt"``, otherwise GMT's default CPT (*turbo*) will be used. If