feat: webhook v2 spec upgrade

[vinayteki95]

Description

• V2 adapter is introduced to send v2 spec events
• Source transformer payloads will be built differently for different specs (v1 and v2)
• Features service will be aware of v2 flag from transformer and pick adapter accordingly

Linear Ticket

Resolves INT-2802

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

Attention: Patch coverage is 91.30435% with 6 lines in your changes missing coverage. Please review.

Project coverage is 74.85%. Comparing base (f22e8f4) to head (4d74019).

Files with missing lines	Patch %	Lines
services/transformer/features_impl.go	25.00%	2 Missing and 1 partial ⚠️
services/transformer/features.go	0.00%	2 Missing ⚠️
gateway/webhook/webhook.go	90.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5224      +/-   ##
==========================================
+ Coverage   74.68%   74.85%   +0.16%     
==========================================
  Files         437      437              
  Lines       61240    61282      +42     
==========================================
+ Hits        45737    45872     +135     
+ Misses      12954    12872      -82     
+ Partials     2549     2538      -11     

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[krishna2020]

features_impl.go returns version based on upgradedToSourceTransformV2 value received by /features response from transformer

when does this come into picture ? and what difference it makes returning v1 vs. v2 here ?