Plugins: Improve the info box for enterprise plugins

[torkelo]

The info box for enterprise plugins shows like warning/error, in open source it should be a more friendly info message I think.

Before:

After:

[mjseaman]

Nice! We discussed adding a "Learn More" button in the top right as well, as the primary action to match that of non-Enterprise plugins. Thoughts?

[sympatheticmoose]

Just for consideration - there is an error state where the user can install the plugin in cloud via grafana.com, but not have entitlement to enterprise plugins. (I'm assuming this is going to be inherited in Enterprise/Cloud).

In principle I'm happy with the shift to a friendlier message though.