ENG-13977: Add deprecation message in existing ELK Terraform

[gabfelp]

Description of the change

We're going to deprecate ELK in the next major due to inconsistencies/confusion between versions v7/v8, so we need to direct users to migrate to custom logging integration instead.

Type of change

• [ ] Bug fix (non-breaking change that fixes an issue)
• [x] New feature (non-breaking change that adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklists

Development

• [ ] Lint rules pass locally
• [ ] The code changed/added as part of this pull request has been covered with tests
• [ ] All tests related to the changed code pass in development

Code review

• [ ] This pull request has a descriptive title and information useful to a reviewer. There may be a screenshot or screencast attached
• [ ] Jira issue referenced in commit message and/or PR title

Testing

Description of testing

[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud