[appmesh-prometheus] Add support for remote-write

[egkelly]

Issue

#977

Description of changes

Add optional configuration for prometheus remote-write according to documentation for Prometheus v2.13. This will need to be changed when the chart installs Prometheus >= 2.26

Checklist

• Added/modified documentation as required (such as the README.md for modified charts)
• Incremented the chart version in Chart.yaml for the modified chart(s)
• Manually tested. Describe what testing was done in the testing section below
• Make sure the title of the PR is a good description that can go into the release notes

Testing

Manually added the remote_write configuration with URL and bearer token directly to a running configuration of appmesh-prometheus and verified successful remote writing to (in my case) NewRelic.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[BennettJames]

Hey egkelly, thanks for submitting a patch.

This looks pretty low risk, so I've approved and merged it.

[egkelly]

Thanks for the speedy PR!