fix: only check for source position when --show-params is set

[gdsoumya]

Fixes #20670

This PR ensures that app get works for multi source apps even when --source-position isn't provided.
Source position check is only necessary if the user also sets --show-params

Checklist:

• Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this does not need to be in the release notes.
• The title of the PR states what changed and the related issues number (used for the release note).
• The title of the PR conforms to the Toolchain Guide
• I've included "Closes [ISSUE #]" or "Fixes [ISSUE #]" in the description to automatically close the associated issue.
• I've updated both the CLI and UI to expose my feature, or I plan to submit a second PR with them.
• Does this PR require documentation updates?
• I've updated documentation as required by this PR.
• I have signed off all my commits as required by DCO
• I have written unit and/or e2e tests for my change. PRs without these are unlikely to be merged.
• My build is green (troubleshooting builds).
• My new feature complies with the feature status guidelines.
• I have added a brief description of why this PR is necessary and/or what this PR solves.
• Optional. My organization is added to USERS.md.
• Optional. For bug fixes, I've indicated what older releases this fix should be cherry-picked into (this may or may not happen depending on risk/complexity).

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[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 55.18%. Comparing base (35b9158) to head (4f311e8).
Report is 373 commits behind head on master.

Files with missing lines	Patch %	Lines
cmd/argocd/commands/app.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #20682      +/-   ##
==========================================
- Coverage   55.20%   55.18%   -0.02%     
==========================================
  Files         324      324              
  Lines       55256    55257       +1     
==========================================
- Hits        30505    30496       -9     
+ Misses      22143    22140       -3     
- Partials     2608     2621      +13     

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[gdsoumya]

/cherry-pick release-2.13