file read sftp validation

[nk1107]

This change adds SFTP credential validations for the AudienceEnteredSFTP action for actions-liveramp-audiences

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

❌ Patch coverage is 87.50000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 79.82%. Comparing base (fc0c26e) to head (65188f6).
⚠️ Report is 36 commits behind head on main.

Files with missing lines	Patch %	Lines
...ns/liveramp-audiences/audienceEnteredSftp/index.ts	87.50%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3098      +/-   ##
==========================================
+ Coverage   79.65%   79.82%   +0.16%     
==========================================
  Files        1133     1165      +32     
  Lines       21026    21512     +486     
  Branches     4070     4154      +84     
==========================================
+ Hits        16749    17172     +423     
- Misses       3577     3626      +49     
- Partials      700      714      +14     

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