docs: add support for langdale (4.1) release

This adds support for the Langdale (4.1) release and update the current
dev branch to Mickledore.

Cc: Quentin Schulz <foss+yocto@0leil.net>
(From yocto-docs rev: 271ae164ba901acacaf2fc910db78246637994aa)

Signed-off-by: Quentin Schulz <quentin.schulz@theobroma-systems.com>
Reviewed-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/set_versions.py

@@ -26,8 +26,8 @@ ourversion = None
 if len(sys.argv) == 2:
     ourversion = sys.argv[1]
 
-activereleases = ["kirkstone", "dunfell"]
-devbranch = "langdale"
+activereleases = ["langdale", "kirkstone", "dunfell"]
+devbranch = "mickledore"
 ltsseries = ["kirkstone", "dunfell"]
 
 # used by run-docs-builds to get the default page
@@ -36,6 +36,7 @@ if ourversion == "getlatest":
     sys.exit(0)
 
 release_series = collections.OrderedDict()
+release_series["mickledore"] = "4.2"
 release_series["langdale"] = "4.1"
 release_series["kirkstone"] = "4.0"
 release_series["honister"] = "3.4"
@@ -65,6 +66,7 @@ release_series["laverne"] = "0.9"
 
 
 bitbake_mapping = {
+    "mickledore" : "2.4",
     "langdale" : "2.2",
     "kirkstone" : "2.0",
     "honister" : "1.52",