make hpa compatible with older k8s versions

[guifl]

Requirements

• [x] I have added test coverage for new or changed functionality
• [x] I have followed the repository's pull request submission guidelines
• [x] I have validated my changes against all supported platform versions

Related issues

https://github.com/launchdarkly/ld-relay-helm/issues/20

Describe the solution you've provided

I've added a check on the k8s version to make sure to use a compatible API version for HPA

Describe alternatives you've considered

Provide a clear and concise description of any alternative solutions or features you've considered.

Additional context

Add any other context about the pull request here.