[FEATURE] Housekeeping - Remove unnecessary github workflow

[mvk-abs]

To avoid that the github workflows are always running as long as we do not need them we remove them completely.

Tasks:

• [x] Remove workflow folder
• [x] Disable mergify

[mvk-abs]

It took not over the needed changes in .projenrc.ts. Need to add it.

• [x] switch off mergify and workflows in .projenrc.ts