Add banner for deprecated custom scan action in SEP

What does this MR do and why?

This MR adds a banner that is displayed when any Scan execution policy contains deprecated custom scan action based on custom_scan deprecated property.

Depends on backend MR: Extend deprecated properties with custom scan a... (!162026 - merged)

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Before	After

How to set up and validate locally

1. Create a project
2. Go to Secure -> Policies and create a new Scan execution policy and use the following YAML:

   type: scan_execution_policy
   name: Custom CI
   description: ''
   enabled: true
   rules:
     - type: pipeline
       branch_type: all
   actions:
     - scan: custom
       ci_configuration: |
         custom_job:
           script:
             - echo "Custom job!"

3. Go back to the policies list and verify that the policy has a deprecation icon and a banner is shown

Related to #477730 (closed)