[FUNK-1643] add bearer token to webhook extensible

[cyberlord29]

Added bearer token support if it is present added it to the auth header

Testing

Include any additional information about the testing you have completed to
ensure your changes behave as expected. For a speedy review, please check
any of the tasks you completed below during your testing.

• Added unit tests for new functionality
• Tested end-to-end using the local server
• [If destination is already live] Tested for backward compatibility of destination. Note: New required fields are a breaking change.
• [Segmenters] Tested in the staging environment
• [Segmenters] [If applicable for this change] Tested for regression with Hadron.

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 2 lines in your changes missing coverage. Please review.

Project coverage is 78.46%. Comparing base (c80d11e) to head (81ba1d6).

Files with missing lines	Patch %	Lines
...tions/src/destinations/webhook-extensible/index.ts	33.33%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2696      +/-   ##
==========================================
- Coverage   78.90%   78.46%   -0.44%     
==========================================
  Files        1089     1036      -53     
  Lines       21361    18716    -2645     
  Branches     4262     3551     -711     
==========================================
- Hits        16854    14685    -2169     
+ Misses       3310     2839     -471     
+ Partials     1197     1192       -5     

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