New object types for representation of creep test on metals

[MarkusSchilling]

As recently announced (see #251 ;)), I would like to add some object types to the bam-masterdata, as well, that are supposed to be used to describe and include data on creep tests (mechanical tests) performed on metals.
Again, the object types are also based on a data schema specifically developed for creep testing. This data schema is published on Zenodo: NFDI-MatWerk/IUC02 Data schema for creep data.

[JosePizarro3]

Thanks a lot @MarkusSchilling

Two questions before reviewing this and #252 (vocabularies):

1. Do you think it makes sense to create a sub-folder ...../datamodel/use_case_creep_test/ where we can move the new object_types.py and vocabularies.py definitions? I think this would be useful to separate developments and make it clearer for you and for others who want to develop use cases (e.g., a subfolder ...../datamodel/use_case_welding/ for @CagtayFabry).
2. Is it ok if I work myself in this and the vocabularies branch? I need to apply formatting, and I will rebase including the new github actions so the pipeline is applied to your pull requests.