Doc: Add export-schema examples

[geographika]

Adds some more examples to gdal vector export-schema.

There are issues when trying to save the output of the command to file using PowerShell, and then using the schema file with gdal vector create. I've documented some (not ideal) workarounds. Maybe it would be possible to have an optional --output-file so GDAL could write directly to a file. Writing directly to the command-line by default is very handy for quickly checking schemas though, so it would be good to leave that as the default.

I added an example of validating output against the schema, but it currently fails with:

  Best Match:
    $.layers[0]: Additional properties are not allowed ('fidColumnName' was unexpected)
  All Errors:
    $.layers[0]: Additional properties are not allowed

I updated the schema to allow for fidColumnName, but this should be reviewed.

Finally, in the pipeline example I was looking for an easy way to rename a field. I used the sql step, which works fine, but was wondering if I was missing an easier/more explicit way of doing this.

Preview at https://gdal--14639.org.readthedocs.build/en/14639/programs/gdal_vector_export_schema.html

[rouault]

Maybe it would be possible to have an optional --output-file

filed as #14640

[geographika]

Thanks @elpaso ! I'll get the latest version and test on Windows, and use this parameter in the example.

[elpaso]

Thanks @elpaso ! I'll get the latest version and test on Windows, and use this parameter in the example.

Thank you for checking this out, please let me know if you find any issues.

[geographika]

Tested on PowerShell versions 5.1 and 7.6.2 - all works fine.

There is Sphinx related issue. I added using the :option:--output option in the PR to link to the option above, however
Sphinx creates a link to option on a different page - https://gdal--14639.org.readthedocs.build/en/14639/programs/gdal_dataset_identify.html#cmdoption-o

This seems to be the case in a few places. I'll open a separate issue for this.

See https://gdal--14639.org.readthedocs.build/en/14639/programs/gdal_vector_export_schema.html#programs/gdal_vector_export_schema-2

[geographika]

Option link fixed (as discussed in #14670). Ready for review from my side.
The main item to check is the fidColumnName fix in the schema.