fix: improve error messaging when mandatory flag is missing in file convert (#1429)

[harshadixit12]

fix: improve error messaging when mandatory flag is missing in file convert (#1429)

When mandatory flags for file convert are missing, the error message is not helpful. In this commit, we have added additional validation to communicate more details in the message.
We have made use of the PersistentPreRunE function in cobra to validate the input passed in to flag.

How I have tested my changes:

• Run file convert command with 'from' and 'to' specified (happy flow) - should not error out
• Run file convert command without specifying the 'to' flag - should return helpful error message.

To do:

• Define what flags we want to validate apart from 'to', and what the error messages should be, and make these changes
• Add tests

[CLAassistant]

All committers have signed the CLA.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 7 lines in your changes missing coverage. Please review.

Project coverage is 29.40%. Comparing base (6d1f171) to head (e489ce3).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/file_convert.go	0.00%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1487      +/-   ##
==========================================
- Coverage   29.43%   29.40%   -0.03%     
==========================================
  Files          61       61              
  Lines        6537     6542       +5     
==========================================
  Hits         1924     1924              
- Misses       4474     4479       +5     
  Partials      139      139              

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[mheap]

Can we expand this to from, and other string flags?