Register “extras” features such as CFs, webhooks, export templates, links, relationships from plugins

[jedelman8]

No description provided.

[glennmatthews]

A plugin might prefer/expect/require certain extensibility features to be defined/enabled as a consequence of installing and enabling the plugin. For example:

• Automatically adding certain custom fields or specific custom links to a Nautobot model(s)
• Automatically defining an export template(s) for a Nautobot model(s)
• Automatically creating certain Relationships between Nautobot models (and/or additional models provided by the plugin itself)

This can actually be implemented today via subclassing the PluginConfig ready() method but we lack documentation and official support for this option. See also #16 as a related issue.

Separate, but closely related, is the idea that plugins should be able to use all of these extensibility features with their own data models, such as change logging of plugin models (#15), webhooks triggered by updates to plugin models (#11), user-defined custom fields and custom links on plugin models (#???), relationships between plugin models (#???)

[glennmatthews]

Addressed in next by #820.