[ci] Create 7.12 branch

Makefile.toml

@@ -3,7 +3,7 @@ default_to_workspace = false
 
 [env]
 # Determines the version of Elasticsearch docker container used
-STACK_VERSION = { value = "7.x-SNAPSHOT", condition = { env_not_set = ["STACK_VERSION"] }}
+STACK_VERSION = { value = "7.12-SNAPSHOT", condition = { env_not_set = ["STACK_VERSION"] }}
 # Determines the distribution of docker container used. Either platinum or free
 TEST_SUITE = { value = "free", condition = { env_not_set = ["TEST_SUITE"] }}
 # Set publish flags to dry-run by default, to force user to explicitly define for publishing