add support for expert (#5036)

* add support for expert

* Refactor elixir expert linter from feedback

- Simplify configuration by removing executable lookup logic
- Update documentation to reflect current configuration options
- Rename test file and update assertions for the new configuration

* default to expert for the lsp

The install instructions included something I missed. It includes a
global install, where the default executable is just `expert`. I'll
default to that and review if I should should add a configuration for a
global config.

---------

Co-authored-by: Your Name <pmonson711@nfiindustries.com>

doc/ale-elixir.txt

@@ -139,8 +139,28 @@ g:ale_elixir_lexical_release
 
   For example, set release to: `/home/projects/lexical/_build/dev/rel/lexical`
 
-  There are currnetly no configuration options for lexical.
+  There are currently no configuration options for lexical.
 
 
+===============================================================================
+expert                                                      *ale-elixir-expert*
+
+Expert (https://github.com/elixir-lang/expert)
+
+                                         *ale-options.elixir_expert_executable*
+                                               *g:ale_elixir_expert_executable*
+                                               *b:ale_elixir_expert_executable*
+elixir_expert_executable
+g:ale_elixir_expert_executable
+  Type: |String|
+  Default: `/usr/bin/elixir-expert`
+
+  Location of the expert executable.
+
+  For example, set release to:
+  `/home/projects/expert/apps/expert/burrito_out/expert_linux_amd64`
+
+  There are currently no configuration options for expert.
+
 ===============================================================================
   vim:tw=78:ts=2:sts=2:sw=2:ft=help:norl:

doc/ale-supported-languages-and-tools.txt

@@ -180,6 +180,7 @@ Notes:
   * `dialyxir`
   * `dogma`!!
   * `elixir-ls`
+  * `expert`
   * `lexical`
   * `mix`!!
 * Elm

doc/ale.txt

@@ -3490,6 +3490,7 @@ documented in additional help files.
     credo.................................|ale-elixir-credo|
     cspell................................|ale-elixir-cspell|
     lexical...............................|ale-elixir-lexical|
+    expert................................|ale-elixir-expert|
   elm.....................................|ale-elm-options|
     elm-format............................|ale-elm-elm-format|
     elm-ls................................|ale-elm-elm-ls|