Add documentation for DANDI models

[candleindark]

This PR adds documentation of the definition and usage of DANDI models.

This PR provides a documentation on how DANDI metadata models are integrated across the DANDI ecosystem. The specific changes are:

1. Adding a new section on models integration
2. Updating the navigation to include this new section
3. Enabling support for mermaid diagrams to display the mermaid diagram in this new section

[satra]

don't we want this to be generated from the linkml automatically? (cc:ing @djarecka )

[yarikoptic]

don't we want this to be generated from the linkml automatically? (cc:ing @djarecka )

this is documentation of the life cycle (where produced, into what form transformed - e.g. jsonschema, used by what - e.g. dandi-cli, web UI, etc) of our metadata model, not documentation/visualization of metadata itself. @candleindark might want to adjust title to make it more explicit.

[candleindark]

don't we want this to be generated from the linkml automatically? (cc:ing @djarecka )

this is documentation of the life cycle (where produced, into what form transformed - e.g. jsonschema, used by what - e.g. dandi-cli, web UI, etc) of our metadata model, not documentation/visualization of metadata itself. @candleindark might want to adjust title to make it more explicit.

File name, heading, and navigation trigger have been modified to reflect the nature of content.

[yarikoptic]

Looks great, thank you @candleindark !

To facilitate demonstration etc, I will just proceed with the merge, but feel welcome to submit improvements in PRs etc.