[Discover] Add registrable DiscoverAction to Discover page

[gaobinlong]

Is your feature request related to a problem? Please describe.
As part of the olly project, the functionalities of generate anomaly detector and text to visualization use LLM to help users to create an anomaly detector and generate visualizations based on natural language, we want to add the entry points of these two functionality to the discover page as follows:

, so in order to implement this, we need to add a registrable DiscoverActions component to DiscoverCanvas, so that other plugins can register their own actions, and then display the actions in the Discover page.

Describe the solution you'd like

Add a registrable DiscoverActions component to DiscoverCanvas.

Describe alternatives you've considered

No other alternatives.

Additional context

The UI mockup:

A demo video:
https://github.com/user-attachments/assets/cd7b3f12-526f-480a-83b2-3623f92ca803