Plugins: Extend panel menu with links from plugins

[jackw]

What is this feature?
This PR adds the functionality for app plugins to add additional menu items to the dashboard panel menu.

In PR #61663 we introduced the plugin extension registry and allowed links to be registered statically via plugin.json. Whilst working on this PR we've decided to remove this in favour of only allowing extension links to be registered via the AppPlugin APIs. We believe this will make it much easier for us and plugin developers to understand and maintain.

The example below show case how to extend the dashboard panel menu with a link:

1. First of all you need to enable preload: true for your plugin. We are collecting the extensions during the preload process of a plugin.
2. Secondly you need to configure an extension for your plugin. Example: https://github.com/grafana/grafana-plugin-examples/blob/mckn/plugin-link-tests/examples/app-basic/src/module.ts
3. You can now navigate to a dashboard and enjoy the power of plugin extensions in the panel menu.

Why do we need this feature?
To improve the user experience by making the UI feel less fragmented into different apps rather than one unified experience.

Who is this feature for?
End users and plugin developers

Which issue(s) does this PR fix?:
Related Epic #61658

Special notes for your reviewer:

Todo:

• Limit the length of the extension title prior to rendering it in the menu.
• Set a max number of items a plugin can add to the menu.
• Add id to the extension so we have something to connect the dynamic part to.
• Running configure function in a context with error handling.
• Make sure that we don't explode if a promise is returned in the configure function.
• Should we allow the path to be configured? Maybe only query string params?
• Make sure that the panel context contains most of the information available in the panel.
• Remove ability to register extension links statically via plugin.json.
• Add validation of the values passed in the configureLinkExtension function.

[github-actions]

⚠️   Possible breaking changes

(Open the links below in a new tab to go to the correct steps)

grafana-data has possible breaking changes (more info)
grafana-runtime has possible breaking changes (more info)

Console output
Read our guideline

[mckn]

⚠️   Possible breaking changes

(Open the links below in a new tab to go to the correct steps)

grafana-runtime has possible breaking changes (more info)

Console output Read our guideline

This feature is not yet released as part of a Grafana version so it is okay for us to break the APIs.

[leventebalogh]

LGTM 🚀