Feature/new custom delete fix #3190

[benjam-es]

This adds a test, using a custom path generator which uses a shared folder (i.e. not individual /1/ folder per image)

Once the test was failing, I extracted out the 'removeFile' and 'removeAllFiles' logic into a FileRemover class using a FileRemover Factory, to work in the same way you currently swap out path generators.

I then added a new FileBasedFileRemover class, which fixes the failing test created to demonstrate #3190.

This PR allows:

• File removal logic can be swapped out
• Existing file removal logic is maintaned in a DefaultFileRemoval class - ensuring everything works as before
• New optional FileBasedFileRemover class allow us to use a custom directory path generator, which does not delete other files with is

These are split into 3 commits to see each part.

[Log1x]

This will be great. I was extremely confused why my entire media library was disappearing... 😩

[elmudometal]

It will take a long time for this to be solved?

[elmudometal]

Do you have any news about this feature?

[benjam-es]

@freekmurze I believe the requests were addressed in April. Let me know if you need anything else.

[freekmurze]

This seems pretty nice!

Could you also write docs on this?

[b-ssr]

Any updates on this?

[benjam-es]

Awaiting @freekmurze approval I believe. I am happy to write docs on it

[freekmurze]

This is looking very good. Could you also add docs for it?

[benjam-es]

@freekmurze I have added a new docs MD file to detail the new functionality

[benjam-es]

It looks like these tests are failing due to this: #3417

[freekmurze]

Thanks!