"Title underline too short" warning in a lot of API docs

[yousefmoazzam]

From browsing the various warnings in the docs build (noted in #468), I noticed these types of warnings for basically every module in httomo:

:mod:`httomo.sweep_runner.param_sweep_yaml_loader`
============================================
/dls/science/users/twi18192/httomo/docs/source/api/httomo.sweep_runner.side_output_manager.rst:2: WARNING: Title underline too short.

It seems this is due to the hardcoded length of the underline in the template used to generate the API docs rst files from*: https://github.com/DiamondLightSource/httomo/blob/18c2e044c0a3c5e3dd831ab7139b1676ba5599bb/docs/source/_templates/module.rst_t#L1-L7

*The -t flag in the docs build script is providing that template I think: https://github.com/DiamondLightSource/httomo/blob/18c2e044c0a3c5e3dd831ab7139b1676ba5599bb/docs/sphinx-build.sh#L28