Keyword arguments for PLAYWRIGHT_PROCESS_REQUEST_HEADERS, pass additional Request fields

[elacuesta]

Deprecate passing arguments positionally to the function defined in PLAYWRIGHT_PROCESS_REQUEST_HEADERS, pass them as keyword instead. Pass additional data about the Scrapy request, not just the headers.

Tasks:

• [x] implementation
• [x] docs
• [x] tests

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 100.00%. Comparing base (5b8cfd7) to head (4098004).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #303 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 6 6 Lines 598 603 +5 ========================================= + Hits 598 603 +5 ```

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