How to install Elasticsearch plugins in offline mode

Issue

Sometimes customers don't have internet connection on their Production environments and want to install in offline mode the required Elasticsearch plugins:
```
analysis-icu, analysis-kuromoji, analysis-smartcn, analysis-stempel
```

We will take analysis-icu as example on how to install it offline (for more details, please see Installing elasticsearch)
First you need to download the correct plugin version, replacing x.x.x (for example: 7.17.9) in the above URL, with the exact Elasticsearch version you use: https://artifacts.elastic.co/downloads/elasticsearch-plugins/analysis-icu/analysis-icu-x.x.x.zip
Once downloaded, add this plugin to your server and use this command to install it offline, replace ${/path/to/plugin.zip} with the correct path:
- Linux OS:
```
sudo bin elasticsearch plugin install file://${/path/to/plugin.zip}
```
- Windows OS:
```
bin\elasticsearch-plugin install file:///${C:/path/to/plugin.zip}
```