Copy known zyte_api_session-prefixed meta into session initialization requests

[Gallaecio]

@VMRuiz reported that, to implement a check method that takes into account meta-defined locations, the init request also needs to have that meta key set. I went a bit further and made it so that any zyte_api_session_-prefixed meta key is copied into the init request, for extra flexibility.

To do:

• Docs about the meta key copy.
• Docs about the need, in these scenarios, to create separate pools per location. Or maybe we should provide a default implementation that does so? Maybe even the ability to set a custom pool through meta? (separate PR)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.56%. Comparing base (7151e73) to head (7780645).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #205   +/-   ##
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  Coverage   97.56%   97.56%           
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  Files          14       14           
  Lines        1476     1476           
  Branches      309      310    +1     
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  Hits         1440     1440           
  Misses         15       15           
  Partials       21       21           

Files	Coverage Δ
scrapy_zyte_api/_session.py	100.00% <ø> (ø)

[Gallaecio]

I’ll keep this PR simple and easy to merge, just copy the 2 known meta keys, and open a separate PR with additional ideas brought up with working on this.