Add support for javalsp configuration options.

This MR adds a new configuration variable `g:ale_java_javalsp_config`
that allows to configure external dependencies and class paths to the
language server.

The variable accepts a dictionary similar to the one supported by the
[vscode/settings.json](https://github.com/georgewfraser/java-language-server#settings)
file.

Deprecates: #2561

doc/ale-java.txt

@@ -131,6 +131,33 @@ executable. For example:
   let g:ale_java_javalsp_executable=/java-language-server/dist/mac/bin/launcher
 <
 
+g:ale_java_javalsp_config                           *g:ale_java_javalsp_config*
+                                                    *b:ale_java_javalsp_config*
+  Type: |Dictionary|
+  Default: `{}`
+
+The javalsp linter automatically detects external depenencies for Maven and
+Gradle projects. In case the javalsp fails to detect some of them, you can
+specify them setting a dictionary to |g:ale_java_javalsp_config| variable.
+>
+  let g:ale_java_javalsp_executable =
+  \ {
+  \   'java': {
+  \     'externalDependencies': [
+  \       'junit:junit:jar:4.12:test',   " Maven format
+  \       'junit:junit:4.1'              " Gradle format
+  \     ],
+  \     'classPath': [
+  \       'lib/some-dependency.jar',
+  \       '/android-sdk/platforms/android-28.jar'
+  \     ]
+  \   }
+  \ }
+
+The Java language server will look for the dependencies you specify in
+`externalDependencies` array in your Maven and Gradle caches ~/.m2 and
+~/.gradle.
+
 ===============================================================================
 eclipselsp                                                *ale-java-eclipselsp*