Migrate NewRelic metrics to NewRelicClientProvider

[snicoll]

The httpClient is now deprecated so we need to migrate to the new API.

As a result, we should double check that the connect-timeout and read-timeout properties are still honoured. If they aren't we need to make sure we add metadata to flag them as error.

[snicoll]

There is a clientProviderType that we may have to expose as well.

[shakuzen]

@neiljpowell has work on this prepared, I believe.
Edit: at least the changes related to NewRelicClientProvider

[neiljpowell]

Hi. Yes, I have a branch and can submit a PR for the new API later today. @shakuzen we'll need to finalize moving the connect/readTimeout into NewRelicConfig or other, per the other Micrometer PR I submitted, at least for the cleanest approach. Not required though.

[snicoll]

Superseded by #20908