feat: add support for headers to source transformation flows

[koladilip]

What are the changes introduced in this PR?

Add support for headers to source transformation flows by exposing them in event context.

What is the related Linear task?

Resolves INT-2504

Please explain the objectives of your changes below

Put down any required details on the broader aspect of your changes. If there are any dependent changes, mandatorily mention them here

Any changes to existing capabilities/behaviour, mention the reason & what are the changes ?

N/A

Any new dependencies introduced with this change?

N/A

Any new generic utility introduced or modified. Please explain the changes.

N/A

Any technical or performance related pointers to consider with the change?

N/A

@coderabbitai review

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Developer checklist

• My code follows the style guidelines of this project

• No breaking changes are being introduced.

• All related docs linked with the PR?

• All changes manually tested?

• Any documentation changes needed with this change?

• Is the PR limited to 10 file changes?

• Is the PR limited to one linear task?

• Are relevant unit and component test-cases added in new readability format?

Reviewer checklist

• Is the type of change in the PR title appropriate as per the changes?

• Verified that there are no credentials or confidential data exposed with the changes.

[devops-github-rudderstack]

Test report for this run is available at: https://test-integrations-dev.s3.amazonaws.com/integrations-test-reports/rudder-transformer/3683/test-report.html

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.62%. Comparing base (c305974) to head (7a8bedd).
Report is 11 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3683      +/-   ##
===========================================
- Coverage    88.63%   88.62%   -0.01%     
===========================================
  Files          592      592              
  Lines        32185    32195      +10     
  Branches      7653     7653              
===========================================
+ Hits         28526    28534       +8     
- Misses        3336     3368      +32     
+ Partials       323      293      -30     

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[sonarqubecloud]

Quality Gate passed

Issues
3 New issues
0 Accepted issues

Measures
0 Security Hotspots
93.4% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud