### Describe Your Changes
Implement spellcheck command:
- add cspell configuration files
- dockerize spellchecking process
- add Makefile targets
This PR adds a standalone `make spellcheck` target to check `docs/*.md` files for spelling
errors. The target process is dockerized to be run in a separate npm environment.
Some `docs/` typo fixes also included.
### 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: Arkadii Yakovets <ark@victoriametrics.com>
Signed-off-by: hagen1778 <roman@victoriametrics.com>
Co-authored-by: hagen1778 <roman@victoriametrics.com>
