### Describe Your Changes
`flagutil.Duration` docs state that `m` suffix stands for `minute`, but
in fact this suffix is not supported due to ambiguity with `month`
### Checklist
The following checks are **mandatory**:
- [x] My change adheres [VictoriaMetrics contributing
guidelines](https://docs.victoriametrics.com/contributing/).
Signed-off-by: Alexander Frolov <winningpiece@gmail.com>
For example, -fooDuration=',10s,' is now supported - it sets three command-line flag values:
- the first and the last one are set to the default value for `-fooDuration`
- the second one is set to 10s
* Introduce flagutil.Duration
To avoid conversion bugs
* Fix tests
* Clarify documentation re. month=31 days
* Add fasttime.UnixTime() to obtain time.Time
The goal is to refactor out the last usage of `.Msecs`.
* Use fasttime for time.Now()
* wip
- Remove fasttime.UnixTime(), since it doesn't improve code readability and maintainability
- Run `make docs-sync` for syncing changes from README.md to docs/ folder
- Make lib/flagutil.Duration.Msec private
- Rename msecsPerMonth const to msecsPer31Days in order to be consistent with retention31Days
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Co-authored-by: Aliaksandr Valialkin <valyala@victoriametrics.com>
