Add fixer for json: python's json.tool (#4847)

Resolves #4314.

Add a fixer that's built into python for json formatting. Include a
couple arguments in docs to make these features more discoverable.

Uses stdin-based fixing so you don't need to save the file to fix.

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

@@ -329,6 +329,7 @@ Notes:
   * `eslint`
   * `fixjson`
   * `jq`
+  * `json.tool`
   * `jsonlint`
   * `prettier`
   * `spectral`