Docs: add initial cookbook section with raster examples

[Sionigdha]

This PR introduces an initial Cookbook section to the GDAL documentation.

What’s included

• New cookbook/ section under doc/source
• Initial structure with:
  • index.rst
  • raster.rst
• Practical, task-oriented examples (CLI + Python style)
• First recipe: raster clipping example

Motivation

This addresses the need for task-based documentation discussed in #12089,
making common GDAL workflows easier to discover and understand.

Scope

• Documentation only
• No code or behavior changes
  Closes Doc: Add "cookbook" section #12089

[jratike80]

I think that cookbook should use the new gdal CLI programs and pipelines. In this case clip and reproject.

[dbaston]

I think a "cookbook" should either reference or include examples from elsewhere in the documentation. Otherwise, we end up having examples split between the cookbook and the reference documentation. Currently we lack a mechanism in Sphinx for this.

[Sionigdha]

Thanks for the feedback! Happy to adapt the examples or structure once there’s agreement on the preferred approach.

[sidhansu10]

Thanks for starting this, the cookbook direction looks very useful. I agree it probably makes sense for cookbook examples to prefer the new gdal CLI where possible, and to keep recipes minimal with links to the relevant reference docs to avoid duplication.
Happy to help with a small follow-up once the structure is settled.