[feature] 'formatter' type plugin like `source` but `format_css:` etc

Would be pretty handy to have some pluggy plugin for reformatting text, for example i want to monitor some pretty messy CSS for a change

the URL in changedetection could be `reformat_css:https://somesite/the-style.css`

then the output is run through `css` reformatter plugin before changedetection

the filters could also be an `include_filter` that is run after all the text and/or html filters are run

additionally, extra filters as part of `include_filters` could run after

https://github.com/dgtlmoon/changedetection.io/blob/01c1ac4c0ca3ddac0205380825b4a5cd5bb82ad1/changedetectionio/processors/text_json_diff/processor.py#L145

ie

`my_custom_filter_plugin:some options..`

and

Start with changedetectionio/processors/text_json_diff/processor.py around line 145, which the issue identifies as the existing filter-processing point. Trace how source URLs and text or HTML filters are handled, then define the formatter and post-filter plugin behavior described here. Done means a CSS formatter URL flow and configurable include filters work without disrupting existing processing.

Written by the indexing model from the issue text.