fix: [CDS-105417]: harness_platform_gitops_applications resource is n…

[mani5h-harness]

…ot detecting drift in application manifest

Title: [Component/Feature] Short Description of the Change

Fix harness_platform_gitops_applications resource is not detecting drift in application manifest.

Summary:
Provide a brief overview of what the PR does and why it is needed.

Issue - harness_platform_gitops_applications resource is not detecting drift in application manifest.
Root cause - ref for sources was being set which is not part of the schema. ref is only used for multisource sources.
Fix - skip setting ref for app source

Details:
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Related Issues:
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Testing Instructions:
Describe how the changes were tested. Include any test cases or steps to verify the functionality.
Please include the below test scenario with your changes.

• Create the resource and execute terraform apply. (Verify the resource is created)
• Execute terraform apply again without any changes. (Verify no changes should be done)
• Update the resource and execute terraform apply. (Verify the resource updated successfully)
• Remove the content from resource file and execute terraform apply. (Verify the resource has been deleted)
• Add again the resource and execute the terraform apply. (Verify the resource is created)
• Verify the import the resource file is working fine.
• In case of remote entity, Verify for both default and non default branch.

Screenshots:
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Checklist:

• Code changes are well-documented.
• Tests have been added/updated.
• Changes have been tested locally.
• Documentation has been updated.

PR Check triggers

• Build: trigger build
• Sub Category Field Check: trigger subcategoryfieldcheck
• gitleaks: trigger gitleaks