### Describe Your Changes
Add support for
https://github.com/VictoriaMetrics/VictoriaMetrics/issues/6930
Calculate `-search.maxUniqueTimeseries` by
`-search.maxConcurrentRequests` and remaining memory if it's **not set**
or **less equal than 0**.
The remaining memory is affected by `-memory.allowedPercent`,
`-memory.allowedBytes` and cgroup memory limit.
### Checklist
The following checks are **mandatory**:
- [x] My change adheres [VictoriaMetrics contributing
guidelines](https://docs.victoriametrics.com/contributing/).
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Signed-off-by: hagen1778 <roman@victoriametrics.com>
Co-authored-by: Roman Khavronenko <roman@victoriametrics.com>
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