Improvements for Dog-Fooding Theia

[tsmaeder]

This epic collects improvements to enable the use of Theia blueprint for developing Theia itself.
See also: #13192

Feature Description:

Blockers

• Breakpoints in plugin-host not hit #12742

Impediments

• Introduce Blueprint Update Channels theia-ide#278
• Allow two installations of Blueprint theia-ide#235
• Run Extension Launch Config Does not Work theia-ide#281

[tsmaeder]

Btw: when I write "blockers" the meaning is "blocking adoption of Theia as the main dev platform for Theia", not that you can't use Theia at all.