docs: updated cmd flags highlight style (#7312)

### Describe Your Changes

Changed highlight style for cmd flags

### Checklist

The following checks are **mandatory**:

- [ ] My change adheres [VictoriaMetrics contributing
guidelines](https://docs.victoriametrics.com/contributing/).

docs/Cluster-VictoriaMetrics.md

@@ -1091,7 +1091,7 @@ Report bugs and propose new features [here](https://github.com/VictoriaMetrics/V
 
 Below is the output for `/path/to/vminsert -help`:
 
-```
+```shellhelp
   -blockcache.missesBeforeCaching int
      The number of cache misses before putting the block into cache. Higher values may reduce indexdb/dataBlocks cache size at the cost of higher CPU and disk read usage (default 2)
   -cacheExpireDuration duration

docs/README.md

@@ -2780,7 +2780,7 @@ Files included in each folder:
 
 Pass `-help` to VictoriaMetrics in order to see the list of supported command-line flags with their description:
 
-```sh
+```shellhelp
   -bigMergeConcurrency int
      Deprecated: this flag does nothing
   -blockcache.missesBeforeCaching int

docs/vmagent.md

@@ -1662,7 +1662,7 @@ It is safe sharing the collected profiles from security point of view, since the
 
 `vmagent` can be fine-tuned with various command-line flags. Run `./vmagent -help` in order to see the full list of these flags with their descriptions and default values:
 
-```sh
+```shellhelp
 ./vmagent -help
 
 vmagent collects metrics data via popular data ingestion protocols and routes them to VictoriaMetrics.

docs/vmalert.md

@@ -1029,7 +1029,7 @@ command-line flags with their descriptions.
 
 The shortlist of configuration flags is the following:
 
-```sh
+```shellhelp
   -clusterMode
      If clusterMode is enabled, then vmalert automatically adds the tenant specified in config groups to -datasource.url, -remoteWrite.url and -remoteRead.url. See https://docs.victoriametrics.com/vmalert/#multitenancy . This flag is available only in Enterprise binaries. See https://docs.victoriametrics.com/enterprise/
   -configCheckInterval duration

docs/vmauth.md

@@ -1170,7 +1170,7 @@ It is safe sharing the collected profiles from security point of view, since the
 
 Pass `-help` command-line arg to `vmauth` in order to see all the configuration options:
 
-```sh
+```shellhelp
 ./vmauth -help
 
 vmauth authenticates and authorizes incoming requests and proxies them to VictoriaMetrics.

docs/vmbackup.md

@@ -325,7 +325,7 @@ Refer to the respective documentation for your object storage provider for more
 
 Run `vmbackup -help` in order to see all the available options:
 
-```sh
+```shellhelp
   -concurrency int
      The number of concurrent workers. Higher concurrency may reduce backup duration (default 10)
   -configFilePath string

docs/vmgateway.md

@@ -270,7 +270,7 @@ Example usage for tokens issued by Google:
 
 Below is the list of configuration flags (it can be viewed by running `./vmgateway -help`):
 
-```sh
+```shellhelp
   -auth.httpHeader string
      HTTP header name to look for JWT authorization token (default "Authorization")
   -auth.jwksEndpoints array

docs/vmrestore.md

@@ -19,7 +19,7 @@ VictoriaMetrics must be stopped during the restore process.
 
 Run the following command to restore backup from the given `-src` into the given `-storageDataPath`:
 
-```sh
+```shellhelp
 ./vmrestore -src=<storageType>://<path/to/backup> -storageDataPath=<local/path/to/restore>
 ```