feat(lazy): add a lazy.lua package descriptor for leaner lazy,nvim-based installation

[noirbizarre]

Hello 👋🏼

Thanks for this plugin.

Here's a small enhancement for lazy.nvim-based installation: this PR adds a lazy.lua package descriptor, which:

• declares the lazy-loading event and cmd
• sets opts_extend by default (no need for the user to add it to its configuration anymore)
• Declare optional dependencies so if they are already present somewhere in the user config, they will be loaded first, even if the user forgot to add them to the dependencies block.

[saghen]

I don't want to set any lazy.nvim definitions by default, especially not for lazy loading. Imo these should be set entirely by the user so it's obvious to them what's happening. Thank you though!