Changed telemetry event type and level to enums.

[danielmorell]

Description of the change

There are two important components to this change.

• It reduces the potential for errors by using enums for the telemetry event type and level.
• It increases the minimum PHP version to 8.1 for the upcoming 4.1 release.

Note: PHP 8.0 stopped receiving security updates in November of 2023. So, it should be safe to drop support for new features like telemetry.

Type of change

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

Related issues

None

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
• "Ready for review" label attached to the PR and reviewers assigned
• Issue from task tracker has a link to this pull request
• Changes have been reviewed by at least one other engineer