Add finder option ref_opt

[wiserfz]

Hi, thank you for such amazing plugin.

I noticed the command lspsaga finder def+ref will display the definition and the references, but the definition also include in the references section:

bashls

rust-analyzer

and I also see the issue #1336 , so I open this PR and add an option finder.ref_opt which indicated the parameters includeDeclaration for the LSP RCP method textDocument/references, the default value is true and also can be a table which can setup value for each LSP client for example:

local saga = require("lspsaga")

saga.setup({
    finder = {
      ref_opt = {
        bashls = false,
        rust_analyzer = false,
        lua_ls = true,
      },
    },
})

bashls

rust-analyzer

lua_ls

Any feedback is appreciated.

[wiserfz]

@glepnir hi, how about this feature? Hope it can be merged.

[glepnir]

LGTM