fix: a lot of small things and adds more customization for caret (#554)

Attention:
prompt_prefix will no longer add a space at the end. So if you still want a space at the end make sure your configuration has one.
The default should not be changed. So if you haven't copied prompt_prefix in your config this doesn't affect you.

Feat:
- prompt prefix does no longer always end with space
- selection_caret configurable. Default: `> `
- result_prefix configurable. Default: `  `
- more actions for git_branches
  - <c-t> does track the branch
  - <c-r> does rebase branch
  - also added delete branch action but not configured. See readme on how to do that

Fixes:
- fix docgen ci
- Better error for lsp_workspace_symbols
- better formatting for CONTRIBUTING.md
- move from systemlist to plenary.job
- git branch now supports checkout on remote branches

lua/telescope/builtin/lsp.lua

@@ -151,8 +151,11 @@ lsp.workspace_symbols = function(opts)
   local params = {query = opts.query or ''}
   local results_lsp = vim.lsp.buf_request_sync(0, "workspace/symbol", params, opts.timeout or 10000)
 
-  if not results_lsp or vim.tbl_isempty(results_lsp) then
-    print("No results from workspace/symbol")
+  -- Clangd returns { { result = {} } } for query=''
+  if not results_lsp or vim.tbl_isempty(results_lsp) or
+     vim.tbl_isempty(results_lsp[1]) or vim.tbl_isempty(results_lsp[1].result) then
+    print("No results from workspace/symbol. Maybe try a different query: " ..
+      "Telescope lsp_workspace_symbols query=example")
     return
   end
 
@@ -167,7 +170,6 @@ lsp.workspace_symbols = function(opts)
     return
   end
 
-
   opts.ignore_filename = utils.get_default(opts.ignore_filename, false)
   opts.hide_filename = utils.get_default(opts.hide_filename, false)