Deprecate addon-links and addon-actions as "built-in addons"

[shilman]

why

Built-in addons are confusing and are only there for backwards compatibility. For example, they generate confusion like this #1016, and multiple cases in the documentation etc.

Currently there are three types of addons:

• "built-in addons" (actions, links)
• "core addons" that are part of the storybooks monorepo but are not included by default (notes, info, etc.)
• "community addons" which are maintained in separate repos by community members

what

I propose we:

• remove actions and links as built-in
• update the docs
• make the actions/links addons like normal "core addons"
• add migration instructions

Alternatively:

• wrap the "built-in" versions with deprecation warnings
• remove them in the 4.0 release (Complete the deprecation of "built-in addons" #1268 = followup)

Old-style code will break, but since we are doing a major version bump that's to be expected and we can add it to the migration guide.

[ndelangen]

I think removing them in 3.0.0 is do-able tbh.

[arunoda]

Okay. This looks great.