Integrate changes of NXem v3

[mkuehbach]

Changes introduced in

• [x] https://github.com/FAIRmat-NFDI/nexus_definitions/pull/254
• [x] https://github.com/FAIRmat-NFDI/nexus_definitions/pull/250
• [x] https://github.com/FAIRmat-NFDI/nexus_definitions/pull/256

demands changes in the template_pathes for all subparsers

• [x] for conventions

• [x] for oasis_eln

• [x] for oasis_config

• [x] axon

• [x] apex

• [x] gatan

• [x] hitachi

• [x] jeol

• [x] nion

• [x] point electronic

• [x] tescan

• [x] tfs

• [x] velox

• [x] zeiss

• [ ] ebsd mtex

• [x] ebsd pyxem

Postponed:

• Add source for each image
• Gatan dims flipped? needs dissimilarly sized examples to test
• Specifically for Zeiss more concepts should be mapped

[mkuehbach]

• [x] Get one example for each file
• [x] Programmatically run tests for all examples (for now via jupyter)