fix: replay request fails with 400 - request neither has anonymousId nor userId

[atzoum]

Description

• Treating replay request types equally to batch request types in terms of expected payload
• Fixing a loopvar issue
• Setting IsProcessorEnabled always true for replay destinations

Linear Ticket

PIPE-351

Security

• The code changed/added as part of this pull request won't create any security issues with how the software is being used.

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (741fd74) 69.14% compared to head (007b00f) 69.17%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3911      +/-   ##
==========================================
+ Coverage   69.14%   69.17%   +0.02%     
==========================================
  Files         353      353              
  Lines       52900    52904       +4     
==========================================
+ Hits        36580    36597      +17     
+ Misses      13999    13990       -9     
+ Partials     2321     2317       -4     

Files	Coverage Δ
backend-config/replay_types.go	100.00% <100.00%> (ø)
backend-config/types.go	88.88% <100.00%> (+0.79%)	⬆️
gateway/handle.go	87.89% <100.00%> (ø)

... and 6 files with indirect coverage changes

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