General: Creator plugins from addons can be registered

[iLLiCiTiT]

Brief description

Addons can register creator plugin paths and Creators can have host name filter.

Description

Creator plugins have host name filtering so e.g. tray publisher creators won't appear in other hosts. Addon can implement new method which return creator plugin paths for specific host name. Default implementation is using get_plugin_paths for backwards compatibility. Installation of openpype plugins will also register creators from modules. Creator plugin has also ability to define host name filter.

Additional information

We wanted to have filtering ability of creator plugins on both addon and creator side so creator plugin has host_name attribute which can define on which host is working. This is for backwards compatibility not abstract. But it is a question if it should be required? In most of cases it is only matter of addon implementation where this filter is "required" (It probably won't happen that host on it's own will register plugins for different host). Also at this time are new creators used only in 3 hosts so it could be easy to change it.

Testing notes:

1. Create addon and add it to addons path
2. Make sure the addon inherit from IPluginPaths
3. Create some creator plugin for TrayPublisher inside the addon
4. Make sure addon implement get_creator_plugin_paths which returns path to the creator dir
5. Run tray publisher
6. The creator should be visible there

Resolves #3165

[ynbot]

Task linked: OP-3220 Creators in Addons issues

[kalisp]

Working for creator in add on.