chore: move fn-in-array to common-functions

This is used by all generic `set` commands, so we should just make it globally available.

plugins/git/subcommands/set

@@ -4,16 +4,6 @@ source "$PLUGIN_CORE_AVAILABLE_PATH/common/property-functions"
 set -eo pipefail
 [[ $DOKKU_TRACE ]] && set -x
 
-fn-in-array() {
-  declare desc="return true if value ($1) is in list (all other arguments)"
-
-  local e
-  for e in "${@:2}"; do
-    [[ "$e" == "$1" ]] && return 0
-  done
-  return 1
-}
-
 git-set-cmd() {
   declare desc="set or clear a git property for an app"
   local cmd="git:set" argv=("$@")