[FEATURE] Add header-file flag to read headers from file

[xbol0]

Description

Add -header-file flag to read headers from file, it's convenient to pass a lot of stationary header params.

I have test it can process FUZZ keyword.

I am considering if it needs header provider to implement instead.

Additonally

• If this is the first time you are contributing to ffuf, add your name to CONTRIBUTORS.md.
  The file should be alphabetically ordered.
• Add a short description of the fix to CHANGELOG.md

Thanks for contributing to ffuf :)

[joohoi]

Thanks for the PR!

I may be missing some use case, so could you enlighten me a bit about a potential situation where using -request does not fill this purpose?