YAML templates docs are dependent on `sphinx-apidoc`

As noted in https://github.com/DiamondLightSource/httomo-backends/issues/10#issuecomment-2443698342, the YAML templates docs are dependent on `sphinx-apidoc`. More specifically, the rst files generated by `sphinx-apidoc` (which is a tool for generating API docs) are modified after `sphinx-apidoc` runs, in order to produce the YAML templates docs.

This approach works decently, but one downside is that API docs are being generated for everything in `httomo_backends/` (none fo which are python packages or modules, there's only some standalone scripts), and so when the final `sphinx-build` command is run in `sphinx-build.sh`, there are some unused API docs rst files that causes some warnings to be outputted:
```
Running Sphinx v8.1.3
loading translations [en]... done
[autosummary] generating autosummary for: api/httomolib.misc.images.rst, api/httomolib.misc.morph.rst, api/httomolib.misc.segm.rst, api/httomolib.prep.phase.rst, api/httomolibgpu.misc.corr.rst, api/httomolibgpu.misc.morph.rst, api/httomolibgpu.misc.rescale.rst, api/httomolibgpu.prep.alignment.rst, api/httomolibgpu.prep.normalize.rst, api/httomolibgpu.prep.phase.rst, ..., api/tomopy.prep.alignment.rst, api/tomopy.prep.normalize.rst, api/tomopy.prep.phase.rst, api/tomopy.prep.stripe.rst, api/tomopy.recon.algorithm.rst, api/tomopy.recon.rotation.rst, api/tomopy.sim.project.rst, backends/templates.rst, index.rst, utilities/yaml_generator.rst
WARNING: Failed to import methods_database.
Possible hints:
* KeyError: 'methods_database'
* ModuleNotFoundError: No module named 'methods_database'
WARNING: Failed to import scripts.yaml_templates_generator.
Possible hints:
* KeyError: 'scripts'
* ModuleNotFoundError: No module named 'scripts'
WARNING: Failed to import scripts.yaml_unsupported_tomopy_remove.
Possible hints:
* KeyError: 'scripts'
* ModuleNotFoundError: No module named 'scripts'
WARNING: Failed to import scripts.
Possible hints:
* KeyError: 'scripts'
* ModuleNotFoundError: No module named 'scripts'
Writing evaluated template result to /dls/science/users/twi18192/httomo-backends/docs/build/_static/nbsphinx-code-cells.css
building [mo]: all of 0 po files
writing output...
building [html]: all source files
updating environment: [new config] 29 added, 0 changed, 0 removed
reading sources... [100%] utilities/yaml_generator
WARNING: autodoc: failed to import module 'methods_database'; the following exception was raised:
No module named 'methods_database' [autodoc.import_object]
WARNING: autodoc: failed to import module 'scripts'; the following exception was raised:
No module named 'scripts' [autodoc.import_object]
WARNING: autodoc: failed to import module 'yaml_templates_generator' from module 'scripts'; the following exception was raised:
No module named 'scripts' [autodoc.import_object]
/dls/science/users/twi18192/httomo-backends/docs/source/api/scripts.yaml_unsupported_tomopy_remove.rst:2: WARNING: Title underline too short.

:mod:`scripts.yaml_unsupported_tomopy_remove`
============================================ [docutils]
WARNING: autodoc: failed to import module 'yaml_unsupported_tomopy_remove' from module 'scripts'; the following exception was raised:
No module named 'scripts' [autodoc.import_object]
looking for now-outdated files... none found
pickling environment... done
checking consistency... /dls/science/users/twi18192/httomo-backends/docs/source/api/methods_database.rst: WARNING: document isn't included in any toctree
/dls/science/users/twi18192/httomo-backends/docs/source/api/scripts.rst: WARNING: document isn't included in any toctree
done
```