Create scan execution policy page [RUN ALL RSPEC] [RUN AS-IF-FOSS]

What does this MR do?

Create scan execution policy page

• YAML only
• generalize form actions from network_policy page
• create :scan_execution_policy_ui feature flag

How to test

https://gitlab.com/-/snippets/2070592

Screenshots (strongly suggested)

Status	Page	Screenshot
w/out :scan_execution_policy_ui	Network Policy
w/out :scan_execution_policy_ui	Scan Execution Policy	N/A
w/ :scan_execution_policy_ui	Network Policy
w/ :scan_execution_policy_ui	Scan Execution Policy

Does this MR meet the acceptance criteria?

Conformity

• I have included a changelog entry, or it's not needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.

Security

Does this MR contain changes to processing or storing of credentials or tokens, authorization and authentication methods or other items described in the security review guidelines? If not, then delete this Security section.

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Related to #273789 (closed)