Memory Inspector not working without electron package

### Bug Description:
For some reason the Memory Inspector is only available in the docker/browser application if we also build the electron application.
On first sight, there seems to be no major difference between the applications.

Needs to be investigated, what causes this behaviour.
Once the issue is resolved, we can ignore `applications/electron` and `theia-extensions/theia-blueprint-updater/` for the docker build.

### Steps to Reproduce:

1. Add `applications/electron` and `theia-extensions/theia-blueprint-updater/` to `.dockerignore`
2. Build the docker image
3. Notice that the memory inspector is not part of the application (Cannot be opened, is not available via `Open view..` and so on.

### Additional Information

- Operating System:
- Theia Version: