Draft: Allow users to configure skip_ci behavior for scan execution policy

What does this MR do and why?

This change adds ability to prevent [skip ci] from skipping scan execution policies.

Users now will have option to prevent skipping pipelines created from scan execution policies with [skip ci] and to specify users that should be exempted from that restriction.

• Add object representation for scan execution policy
• Add more generic ExecutionPolicies::PipelineContext
• Refactor PipelineContext and split it up for:
  • Pipeline execution policies
  • Scan execution policies
• Move existing logic from Processor to ScanExecutionPolicies::PipelineContext
• Extend schema for scan execution policies with skip_ci option
• Prevent [ci skip] if any applicable scan execution policy has this option enabled

References

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• Allow users to configure skip ci behavior for p... (!173480 - merged)

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Related to #482952 (closed)