Add PLUMED ContentTypes

[UlrikeS91]

from issue #7

Resources:

• https://www.plumed.org/
• https://www.plumed.org/doc-v2.9/user-doc/html/index.html
• https://www.plumed-nest.org/plumed.html
• https://search.kg.ebrains.eu/instances/0f3de301-da29-4836-bc1c-5ca7b363f8e4 (KG model)

Info:

• PLUMED = PLUgin for MolEcular Dynamics
• "PLUMED is a plugin that works with a large number of molecular dynamics codes (Codes interfaced with PLUMED)"

Instances:
It's a plugin and I'm not sure if there are any relevant content types for it, but I linked the PLUMED-NEST webpage as an example and because the KG model links to it. This may have its own content types or the same as the normal NEST, jus that we need to add "plumed".
e.g., application_vnd.plumednest (vs. application_vnd.nest)