Abstract out unsupported attribute finder

What does this MR do and why?

Describe in detail what your merge request does and why.

Abstract out unsupported attribute finder

• implement it for scan execution policies
• while each policy type will have different attributes, abstracting out a general "is there attributes that don't below" method seems reasonable to me
• more policy-specific checks can be done in the policy-specific fromYaml methods (something like the below)
• I don't see there being a performance issue to loop through all the attributes of the policy multiple times (once in hasUnsupportedAttribute and more in policy-specific checks) as the policies have very few attributes

// scan_execution_policy/lib/fromYaml.js

const policySpecificCheck(policy) { /** does a policy-specific check **/ };

export const fromYaml = (manifest) => {
  ...
  return hasUnsupportedAttribute({ policy, primaryKeys, rulesKeys, actionsKeys }) || policySpecificCheck(policy) : ...

NOTE: This is not supposed to catch all use cases! A user can input whatever they want in YAML (much of which would not be caught by this) and that would be better caught by schema validation (issue: FE: Validation prevents user from submitting po... (#369007 - closed)), but this MR is an acceptable first step. Schema validation is currently not working and is being fixed by Upgrade monaco-yaml and re-enable schema valida... (!96385 - merged).

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Scenario	Screenshot
Wrong primary keys
Wrong rule keys
Wrong action keys

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Upload a GitLab Ultimate license
2. Turn on the :scan_execution_rule_mode feature flag
3. Navigate to a project => Security & Compliance => Policies => New policy => Scan Execution Policy => yaml mode
4. Add WRONG_KEY: "this is wrong and should result in the rule mode being disabled" to the yaml in between another primary/rule/action key
5. Navigate back to rule mode
6. Verify the rule mode is disabled

Sample yamls that have unsupported keys

Unsupported primary key

type: scan_execution_policy
name: ''
WRONG: THIS_IS_WRONG
description: ''
enabled: true
rules:
  - type: pipeline
    branches: []
actions:
  - scan: dast
    site_profile: ''
    scanner_profile: ''

Unsupported rule key

type: scan_execution_policy
name: ''
description: ''
enabled: true
rules:
  - type: pipeline
    branches: []
    WRONG: THIS_IS_WRONG
actions:
  - scan: dast
    site_profile: ''
    scanner_profile: ''

Unsupported action key

type: scan_execution_policy
name: ''
description: ''
enabled: true
rules:
  - type: pipeline
    branches: []
actions:
  - scan: dast
    site_profile: ''
    scanner_profile: ''
    WRONG: THIS_IS_WRONG

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #359887 (closed)