Fix `compactor_blocks_retention_period` type in `extra_small_user`

[kavirajk]

The actual type of compactor_blocks_retention_period is model.Duration. Which comes from prometheus common package.

The problem is that model.Duration have custom JSON unmarshal which treat the incoming value as string. https://github.com/prometheus/common/blob/main/model/time.go#L276

So setting it as integer, won't work when unmarshalling with JSON.

NOTE: This won't be an issue for YamlUnmarshal, as it always treating it as string (even though you put it as integer) https://github.com/prometheus/common/blob/main/model/time.go#L307

What this PR does:

Which issue(s) this PR fixes: Fixes NA

Checklist

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