refactor!: deprecate telescope 'theme' option

Pass the theme options in directly now. For example:
```lua
require('dressing').setup({
  select = {
    telescope = require('telescope.themes').get_ivy({})
  }
})
```

lua/dressing/config.lua

@@ -45,12 +45,9 @@ local default_config = {
     backend = { "telescope", "fzf_lua", "fzf", "builtin", "nui" },
 
     -- Options for telescope selector
-    telescope = {
-      -- can be 'dropdown', 'cursor', or 'ivy'
-      -- or you can use a configuration directly:
-      -- theme = require('telescope.themes').get_ivy({...})
-      theme = "dropdown",
-    },
+    -- These are passed into the telescope picker directly. Can be used like:
+    -- telescope = require('telescope.themes').get_ivy({...})
+    telescope = nil,
 
     -- Options for fzf selector
     fzf = {
@@ -135,6 +132,13 @@ M.update = function(opts)
     )
   end
 
+  if newconf.select.telescope and newconf.select.telescope.theme then
+    vim.notify(
+      "Deprecated: dressing.select.telescope.theme is deprecated. Pass in telescope options directly (:help dressing)",
+      vim.log.levels.WARN
+    )
+  end
+
   for k, v in pairs(newconf) do
     M[k] = v
   end

lua/dressing/select/telescope.lua

@@ -21,19 +21,27 @@ M.select = function(config, items, opts, on_choice)
     }
   end
 
-  local theme
-  local ttype = type(config.theme)
-  if ttype == "string" then
-    theme = themes[string.format("get_%s", config.theme)]
-  elseif ttype == "function" then
-    theme = config.theme
-  else
-    theme = function(s)
-      return vim.tbl_extend("keep", s, config.theme or {})
+  local picker_opts = config
+
+  if picker_opts == nil then
+    -- Default to the dropdown theme if no options supplied
+    picker_opts = themes.get_dropdown()
+  elseif config.theme then
+    -- Backwards compatibility for the `theme` option
+    local theme
+    local ttype = type(config.theme)
+    if ttype == "string" then
+      theme = themes[string.format("get_%s", config.theme)]
+    elseif ttype == "function" then
+      theme = config.theme
+    else
+      theme = function(s)
+        return vim.tbl_extend("keep", s, config.theme or {})
+      end
     end
-  end
 
-  local picker_opts = vim.tbl_extend("keep", config, theme({}))
+    picker_opts = vim.tbl_extend("keep", config, theme({}))
+  end
 
   pickers.new(picker_opts, {
     prompt_title = opts.prompt,