Update Approval Process in Contribution Guide - Labeling Proposal+

[BirgitBoss]

For preparation to do more and more specification work in github itself (up to now published pdf of the specification was the master) we need to have an approval process that is compliant to the approval processes as defined by IDTA and Plattform Industrie 4.0 for joint working groups.

proposal is to have the labels as defined in https://github.com/OpenManufacturingPlatform/sds-bamm-aspect-meta-model/blob/main/CONTRIBUTING.md#labeling

This proposal requires to clearly identify bugs as requested in #52

[g1zzm0]

Is there a use case where we need labeling?