Directly embed JetBrains Gateway download on workspace loading screen

[loujaybee]

Currently when opening a JetBrains IDE from the browser, the user is prompted to install the gateway, however that user has to leave the browser, go to JetBrains docs (Figure 1), find the right download, and install it. Instead we could directly offer users the JetBrains Gateway download from within the workspace start page (Figure 2), this will reduce the number of steps to use JetBrains with Gitpod.

Relates to:

• Prompt when desktop IDE not installed (or open), e.g. "scheme does not have a registered handler" #9975
• Track when Desktop IDE URI redirect fails #9934

Figure 1	Figure 2

Related slack conversation.

[stale]

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[loujaybee]

Linking related comment:

I'm still uncomfortable with that. Because without toolbox users cannot upgrade Gateway and it will case an issue with each major release. We could insert direct links to toolbox downloadable instead? I think this can be done as another PR though - @akosyakov

#12082 (comment)