Add a command to install a plugin only on the website

[anna-geller]

Feature description

This PR kestra-io/kestra#2967 adds valuable extra information on how to install a plugin. However, we need to find a way to only include it on the website, not within the application's documentation, as the plugin is already installed there.

Potential solution:

• find a way only to inject it on the website inline e.g., before the Properties section
• find a way to add this on the sidebar of the plugin documentation on the website only