Add blockmedian and surface gallery example

[Aayush7788]

Description of proposed changes

Adds a gallery example showing how to reduce irregular bathymetry observations
with pygmt.blockmedian before interpolating them with pygmt.surface.

The example uses the built-in bathymetry sample dataset and compares the reduced
observations with the resulting grid.

Fixes #1352

Preview: https://pygmt-dev--4771.org.readthedocs.build/en/4771/gallery/images/gridding_with_surface.html

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[seisman]

It seems the -C option is not aliased in PyGMT yet. Would you like to add it in a separate PR?

[Aayush7788]

thanks for pointing this out; I’ll keep this PR focused on the gallery example and leave the alias for a separate contribution.

[seisman]

This example already looks good, but we need to implement the -C alias before merging this PR.

[Aayush7788]

Understood. I’ll implement the -C alias in a separate PR first. Before I start, could you please confirm that the public parameter should be named center and that it should be added consistently to blockmean, blockmedian, and blockmode, since GMT supports -C in all three modules? After that PR is merged, I’ll update this example to use center=True.

[seisman]

Yes. If you look at the source code, you’ll notice that there are currently two ways to add the -C alias because we are transitioning from the old alias system to the new one: (1) using the use_alias decorator and (2) using the AliasSystem class. The use_alias decorator belongs to the old system and is no longer recommended, so please add the alias using AliasSystem instead.

[Aayush7788]

I opened #4780 to add the center parameter to blockmean, blockmedian, and blockmode using AliasSystem.

[seisman]

Please merge the main branch into this branch, and then update C=True to center=True.

[Aayush7788]

@seisman , any update

[Aayush7788]

@seisman, any update on this branch?