Add subcommands parameter for module alternatives. (#4654)

* Add slaves parameter for module alternatives.

* alternatives: Improve documentation abous slaves parameter

* alternatives: Apply suggestions from code review

Co-authored-by: Felix Fontein <felix@fontein.de>

* alternatives: Add schangelog for slaves parameter

* alernatives: Add integration tests

* alternatives: Improv tests

* alternatives: Update tests/integration/targets/alternatives/tasks/slaves.yml

Co-authored-by: Felix Fontein <felix@fontein.de>

* alternatives: Rework logic to support updating priority and subcommands

* alternatives: Use more inclusive naming

* alternatives: Fix linter warnings

* alternatives: Dont fail if link is absent

* alternatives: Update changelog fragment

* alternatives: Add tests for prio change and removing

* alternatives: Apply suggestions from code review

Co-authored-by: Felix Fontein <felix@fontein.de>

* alternatives: Add `state=auto`to reset mode to auto

* alternatives: Fix linter warnings

* alternatives: Fix documentation.

* alternatives: Combine multiple messages.

* alternatives: Set command env for all commands.

* alternatives: Do not update subcommands if parameter is omited

* alternatives: Fix a bug with python 2.7 var scoping

* alternatives: Improce diff before generation

* alternatives: Fix linter warnings

* alternatives: Fix test names

* alternatives: Simplify subcommands handling and improve diffs

* aliases: Only test for subcommand changes if subcommands parameter is set.

* Update plugins/modules/system/alternatives.py

Co-authored-by: Felix Fontein <felix@fontein.de>

* Apply suggestions from code review

Co-authored-by: Felix Fontein <felix@fontein.de>

.github/BOTMETA.yml

@@ -1027,7 +1027,7 @@ files:
   $modules/system/alternatives.py:
     maintainers: mulby
     labels: alternatives
-    ignore: DavidWittman
+    ignore: DavidWittman jiuka
   $modules/system/aix_lvol.py:
     maintainers: adejoux
   $modules/system/awall.py: