Add ability for metris to be disabled

[allada]

Adds the ability to disable metrics through env via TURBO_CACHE_DISABLE_METRICS or through config file.

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This change is 

[allada]

+@chrisstaite-menlo

Reviewable status: 0 of 6 files reviewed, all discussions resolved (waiting on @chrisstaite-menlo)

[chrisstaite-menlo]

I wonder, should metrics always be disabled when there's no service and enabled when there's at least one?

[chrisstaite-menlo]

cas/cas_main.rs line 432 at r1 (raw file):

        metrics_enabled = false;
    }
    let runtime = tokio::runtime::Builder::new_multi_thread()

I think if there's no server specified then metrics should be disabled too.

[chrisstaite-menlo]

Reviewed 6 of 6 files at r1, all commit messages.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @allada)

[allada]

Done.

Reviewable status: 4 of 6 files reviewed, 1 unresolved discussion (waiting on @chrisstaite-menlo)

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cas/cas_main.rs line 432 at r1 (raw file):

Previously, chrisstaite-menlo (Chris Staite) wrote…

I think if there's no server specified then metrics should be disabled too.

Done.

[chrisstaite-menlo]

Reviewed 2 of 2 files at r2, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @allada)