fix: validate presence of flags and args in file patch command

[Prashansa-K]

The command intends to patch input files either via selector-value flags or patch file arguments. The change ensures that at least one of these is present, but not both at the same time. Till now, the command accepted patches from flags and patch files at the same time, but ignored the patches passed via flags. This was a confusing behaviour for customers.

Fix #1130

@rspurgeon I have created a new issue for patch file validation here.
We can discuss its feasibility and usecase there. For this particular issue (#1130), I felt erroring out with a proper reasoning given to user should be the best way to move forward.

[Prashansa-K]

Here's the command in action:

[GGabriele]

Changes look good to me!

Nit: can you please make sure commit messages follow the convention even for body length? e.g. The body of your message should not contain lines longer than 72 characters

This makes everything more readable.

For example:

commit a0388610ea9dc259e14c205e85811aac8bd7ed10
Author: Gabriele Gerbino <gabrielegerbino@gmail.com>
Date:   Fri Mar 15 12:57:02 2024 +0100

    fix: do not fetch kong version when running `validate`

    decK used to fetch the running Kong version in order to gate
    route regex patterns validation. This is problematic in
    the case users don't have access to the `/` endpoint, which
    is the one used to fetch the version of the runtime.

    This commit removes the need of fetching the Kong version
    entirely by relying on the `_format_version` field from the
    config file instead.

vs.

commit 47ab479635509980b1ba7ca6b42e5e28bc443789
Author: Prashansa Kulshrestha <prashkulshrestha@gmail.com>
Date:   Thu Jul 18 10:47:17 2024 +0530

    fix: validate presence of flags and args in file patch command

    The command intends to patch input files either via selector-value flags or patch file arguments. The change ensures that at least one of these is present, but not both at the same time. Till now, the command accepted patches from flags and patch files at the same time, but igno
red the patches passed via flags. This was a confusing behaviour for customers.

    Fix #1130

[codecov-commenter]

Codecov Report

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

Project coverage is 22.43%. Comparing base (0cdef1e) to head (cbe47e0).

Files	Patch %	Lines
cmd/file_patch.go	0.00%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1342      +/-   ##
==========================================
+ Coverage   22.39%   22.43%   +0.04%     
==========================================
  Files          54       54              
  Lines        4515     4520       +5     
==========================================
+ Hits         1011     1014       +3     
- Misses       3404     3407       +3     
+ Partials      100       99       -1     

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[Prashansa-K]

Updated the commit message.