:recycle: move metrics into one file

[joerunde]

Motivation

This PR accomplishes two things:

• Upgrades the metrics crate to the latest version, which causes API breaking changes
• Duplicates all counter metrics to include {metric_name}_total to align with the prometheus metrics exported by vLLM

Modifications

This refactors all usages of the metrics crate into a single file, so that changes to how it's used can be made in one place. This lets us easily duplicate all the counter metrics.

Result

No existing behavior should change, only new *_total counters should be added to the /metrics endpoint.

[joerunde]

Here's an example output of /metrics from running locally: metrics.txt

[joerunde]

TravisCI test run here: https://v3.travis.ibm.com/github/ai-foundation/fmaas-inference-server/builds/19285089 (using a build pushed from this branch)

Seems to work fine on the dev pod 🤞🤞🤞