Update metric names for Otel conventions

[CVanF5]

Proposed changes

In an effort to be more consistent with the use of "count" and pluralization the following changes were made:

1. Where "count" is used, ensure the type is "gauge" and not "sum"
2. Where "count" is used remove pluralization from the name.
3. Pluralization consistency. If the last word is a plural ensure the type is "sum"
4. Fix unit names where applicable
5. Where the unit is "bytes" remove byte from the name
6. Replace abbreviated TX/RX with words

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING document
• I have run make install-tools and have attached any dependency changes to this pull request
• If applicable, I have added tests that prove my fix is effective or that my feature works
• If applicable, I have checked that any relevant tests pass after adding my changes
• If applicable, I have updated any relevant documentation (README.md)
• If applicable, I have tested my cross-platform changes on Ubuntu 22, Redhat 8, SUSE 15 and FreeBSD 13

[CodeMonkeyF5]

For the nginx.* metrics involving potential IO with both direction of either RX or TX need to know whether or not bi-directional is involved:

• nginx.http.request.byte.io
• nginx.stream.byte.io
• nginx.http.upstream.peer.byte.io

If these are one direction only shouldn't need an attribute like nginx.io.direction and could include it in the name (e.g. nginx.stream.io.sent).

Ideally those metrics would also be consistent with the OTel attribute values and not use the abbreviated form of "RX" or "TX" and instead use "receive" and "transmit".

For any of the metric names containing the word "byte", this isn't really something we should use since the Unit (UCUM) describes that. So could go through and revise any that have ".byte" appearing in the name?

[CodeMonkeyF5]

LGTM!