Make phpactor configurable and documented (#5027)

Add php_phpactor_executable for phpactor and make it configurable
through php_phpactor_config.

When phpactor was first added in 3b8ff65, it had no configuration. Thus
the documentation for it could be completely blank. That is why it now
seems like an initial addition

Co-authored-by: cos <cos>

doc/ale-php.txt

@@ -78,6 +78,36 @@ g:ale_php_phan_use_client
   instead of the phan standalone.
 
 
+===============================================================================
+phpactor                                                     *ale-php-phpactor*
+
+                                          *ale-options.php_phpactor_executable*
+                                                *g:ale_php_phpactor_executable*
+                                                *b:ale_php_phpactor_executable*
+php_phpactor_executable
+g:ale_php_phpactor_executable
+  Type: |String|
+  Default: `'phpactor'`
+
+  This variable sets executable used for phpactor.
+
+php_phpactor_init_options
+g:ale_php_phpactor_init_options
+  Type: |Dictionary|
+  Default: `'{}'`
+
+  This variable can be changed to customize the LSP initialization_options.
+  For example: >
+
+  let g:ale_php_phpactor_init_options = {
+  \   'language_server_phpstan.enabled': v:false,
+  \   'language_server_psalm.enabled': v:false,
+  \   'worse_reflection.stub_dir': '%application_root%/.php-stubs'
+  \}
+<
+For all available options and explanations, visit
+https://phpactor.readthedocs.io/en/master/reference/configuration.html
+
 ===============================================================================
 phpcbf                                                         *ale-php-phpcbf*
 

doc/ale.txt

@@ -3760,6 +3760,7 @@ documented in additional help files.
     cspell................................|ale-php-cspell|
     langserver............................|ale-php-langserver|
     phan..................................|ale-php-phan|
+    phpactor..............................|ale-php-phpactor|
     phpcbf................................|ale-php-phpcbf|
     phpcs.................................|ale-php-phpcs|
     phpmd.................................|ale-php-phpmd|