Separate public route for external apps

[diocas]

Quick fix to ensure that we redirect users to the idp when trying to open files with external apps that are not from public links.

Fixes #6069
Potentially fixes #6045

[update-docs]

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[sonarqubecloud]

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[ishank011]

@diocas we also need to pass the public-token header for public links, right?

[ishank011]

@diocas we also need to pass the public-token header for public links, right?

This is already there, looks good

[pascalwengerter]

@diocas this one needs a rebase since we merged a big PR changing routes yesterday:)

[diocas]

@pascalwengerter @fschade PR updated

[diocas]

Superseded by #6314