Override exporter: expose all fields that can be converted to float64

[SungJin1212]

The current override-exporter only exposes a limited set of fields. This PR changes the logic to expose all fields that can be converted to a float64 type.

For reviewers: Would it be better to expose only the metrics that have values different from their defaults?

Which issue(s) this PR fixes:
Fixes #

Checklist

• Tests updated
• Documentation added
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]

[friedrichg]

please take a look @bogdan-st

[bogdan-st]

Well I don't have much to say other than LGTM

[danielblando]

For reviewers: Would it be better to expose only the metrics that have values different from their defaults?

I like to export even default so we can have data of which value is actually configured, but for another point, I am worry about number of metrics that we gonna start generating. Do we want to start exposing all this metrics? Is there a valid cases for this? In cases where we have hundreds or thousands of tenants, this can explode. For prometheus that is not a real problem

[SungJin1212]

@danielblando
I think it's good to expose default values. But since we're exposing the cortex_overrides metric only for tenants registered in the runtime config, I'm wondering if this could cause a series explosion. WDYT?

[danielblando]

@SungJin1212
Ah I missed that. Valid point. I think it is fine then, but it makes sense to not export default if we are just exporting override tenants. If not exported we can assume it is the default i guess

[SungJin1212]

@danielblando
Let's go with this for now, and if we need to expose the default later, we can do so.