[Feature] universal fzf: use one command to `fzf` sources of many different categories

When I use `fzf`, before I pressing the command, I always need to think about what I am search for. The thing I am searching for belongs to files, buffers, colorscheme, lsp symbols, tags, or other categories. This process was very interrupting to me. I think we can have a `ctrl-p`. It is a single command that can return all buffers, files, tags, or whatever I want. so that when we want `fzf`, we only need to press that command without thinking. fzf is fast and we can use this.

To do this, we need to build `action` `preview` and other things dynamicly, can we achieve it?