Auto install bundle

Automatically install extensions "bundled" with installer on startup.

**Issues**:
* Should appReady in ExtensionManger be used instead?

cc @dangoor @peterflynn 

This is for #9233 

### Testing Matrix for `auto-install-extensions` folder

#### Should fail silently
* is missing
* is empty
* contains file which have non-zip file extension
* contains file which have non-extensions with zip file extension
* contains extension that are already installed
* contains extension that has a newer version installed

#### Should install extension
* contains extension that is not yet installed
* contains extension that has an older version installed

Done, but I indented everything to same level.