Implement workspace heartbeats for Jetbrains IDEs

[atduarte]

To avoid the workspace timing out while the user is using the Jetbrains local IDE, we must send heartbeats to Gitpod when there's user activity locally.

Proposed solution
Install a plugin in the Jetbrains IDE backend that listens to activities such as "FileOpened" and sends heartbeats to the Gitpod server.

[akosyakov]

/schedule

[roboquat]

@akosyakov: Issue scheduled in the IDE team (WIP: 0)

In response to this:

/schedule

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[akosyakov]

/assign @atduarte