Add ability to selectively remove middlewares from apiFetch

[coderGtm]

What?

Closes #16805

Added ability to selectively remove/unregister middleware(s) from apiFetch.

Why?

There exists no way to remove middlewares used in apiFetch and this was a blocker in many use cases as discussed in length in #16805

There was also an earlier PR (#16806) to fix this issue but was somehow closed without merging. The approach taken in this PR is slightly different.

How?

• Added a getMiddleware() function that returns the middlewares used to users.
• Added a removeMiddleware() function to remove middlewares using the middlewares returned from above.

Testing

I have added a couple of tests in the tests file for this feature.

[github-actions]

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[github-actions]

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[github-actions]

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[coderGtm]

Is there anything else required to move this forward? I am fairly new to WordPress Contribution so would appreciate any guidance.

TIA

cc: @nerrad @mmtr