T7981: prs conflict check workflow updated to use schedule checks

[kumvijaya]

Change summary

PR Conflict Check Workflow - Updated for Scheduled Execution and Removed mergify based check.

Enhanced the PR conflict checking workflow to support scheduled and manual triggers, addressing the issue where GitHub's mergeable state is unreliable immediately after commits.

The scheduled approach will help to solve the issue where immediate post-commit checks don't provide accurate merge status, ensuring comprehensive and reliable conflict detection.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe):

Related Task(s)

https://vyos.dev/T7981

Related PR(s)

How to test / Smoketest result

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• I have run the components SMOKETESTS if applicable
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly

[github-actions]

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