Codelens support

[shinzui]

Is your feature request related to a problem? Please describe.
It would be nice to support codelens actions.

Describe the solution you'd like

Support displaying codelenses in virtual text and a way to run the code lens actions.

[kkharji]

For the display of codelens, I have vim.lsp.codelens.refresh() on lsp attach function. Though, we might endup with better user experience if it got manged by lspsaga

For supporting code lens actions, I had tried to tackle this before and merge both code actions and codelens in one command because it makes sense. https://github.com/simrat39/rust-tools.nvim/pull/84/files.

It's fairly easy to port it here because that PR still uses lspsaga api. However, I won't be able to do that anytime soon, let alone completing the PR (@simrat39 the next rust project I work on, I'll test, resolve conflicts and remove lspsaga api ).

@shinzui feel free to contribute.