The purpose of this change is to reduce confusion between using
`flag.Duration` and `flagutils.Duration`. The reason is that
`flagutils.Duration` was mistakenly used for cases that required `m`
support. See
ab0d31a7b0
The change in name should clearly indicate the purpose of this data
type.
### Describe Your Changes
Please provide a brief description of the changes you made. Be as
specific as possible to help others understand the purpose and impact of
your modifications.
### Checklist
The following checks are **mandatory**:
- [ ] My change adheres [VictoriaMetrics contributing
guidelines](https://docs.victoriametrics.com/contributing/).
Signed-off-by: hagen1778 <roman@victoriametrics.com>