[ENHANCEMENT] add native support for Identity CORS configuration

[daniel-ewing]

Describe the use case:

This issue Invalid CORS Request is frequently occurring, especially with AWS ALB.

Describe the enhancement/feature:

Add native support the the 10.x helm charts to configure Identity CORS setting without using these undocumented env vars:

identity:
  env:
    - name: IDENTITY_CORS_ALLOWED_ORIGIN_PATTERNS
      value: *test.com,*another*.com
    - name: IDENTITY_CORS_ALLOWED_METHODS
      value: GET,POST

Which are in the config:

identity:
  cors-allowed-origin-patterns: ""
  cors-allowed-methods: ""

Desired outcome and acceptance tests:

### Tasks
- [ ]  I can reproduce Identity `Invalid CORS Request` error, e.g.: as shown in [SUPPORT-22437](https://jira.camunda.com/browse/SUPPORT-22437).
- [ ] I can configure Identity CORS setting in my values.yaml file without using env vars.
- [ ] After applying the new settings via `helm upgrade`, the Identity `Invalid CORS Request` error is resolved.
- [ ] No other Identity env vars are affected.

[aabouzaid]

@jessesimpson36 Suggested a really good idea for this: a way to append any extra config without rebuilding the whole config, as we do in identity.configuration (also for all apps).