helper/metricsutil: Update usage of expfmt

[peteski22]

The previously exposed constants are no longer exposed, and we can use expfmt.Format instead. prometheus/common#576

Once Prometheus gets updated, the Vault dependency breaks.

Authored by @metalmatze in (#25799)

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Build Results:
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[github-actions]

CI Results:
All Go tests succeeded! ✅

[jimmybigcommerce]

Wondering why this change hasn't made it into a tagged release yet?

[peteski22]

@jimmybigcommerce I believe it is part of 1.16.2.

https://github.com/hashicorp/vault/releases/tag/v1.16.2

[jimmybigcommerce]

@jimmybigcommerce I believe it is part of 1.16.2.

https://github.com/hashicorp/vault/releases/tag/v1.16.2

This line appears to be the old code:
https://github.com/hashicorp/vault/blob/v1.16.2/helper/metricsutil/metricsutil.go#L148

[peteski22]

@jimmybigcommerce I believe it is part of 1.16.2.
https://github.com/hashicorp/vault/releases/tag/v1.16.2

This line appears to be the old code: https://github.com/hashicorp/vault/blob/v1.16.2/helper/metricsutil/metricsutil.go#L148

'doh' you're right I made a mistake when searching the PR number (missed the 7 from the end 🤦🏼), my apologies.

It's not not in any release as of yet, the reason is likely to be code freezes and such relating to the timing of the last release. I'd expect to see it in a future tagged release as it's part of main now.

😄