Graph: Add sample data

[flash1293]

This PR adds sample Graph workspaces to the existing sample data sets.

If the license level is sufficient, a Graph link also shows up in the sample data panel:

Known limitations: As the current API of the home plugin does not allow de-registering a link from the sample dataset panel, the following (unlikely) scenario exists:

• User goes platinum
• User installs sample data
• User changes license to something below platinum (e.g. Basic)
• Kibana server is not restarted
• Graph link in the sample data panel is still shown and leads to a "Get a platinum license to use Graph" error message if clicked

I think this is OK, as the user had platinum at one point and this can be seen as an additional way of advertising the feature.

Alternatively the home API can be extended to also be able to remove links from the sample data panels, but that felt like over-engineering.

cc @shaunmcgough

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: 632c00f

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@elasticmachine merge upstream

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)

[nickofthyme]

Nice! Tested locally with no issues with and without trial license. 👍

[kertal]

Code LGTM, great that there are now examples in Graph, this is very useful for demoing and new users 👍
I've noticed one more minor limitation, when you've got already installed demo data, the links to graph workspaces from home don't work, however, in that case it's easy to fix by the user by reinstalling the demo data

[kertal]

I'm not 100% sure, but "The thicker the line is, there are more correlated documents between the vertices." sounds a bit like german (also like austriakisch)

[flash1293]

Hehe, ping @shaunmcgough - these are your German roots shining through.