chore(self-hosted): use /bin/sh shebang in kong-entrypoint.sh (#46897)

docker/volumes/api/kong-entrypoint.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/bin/sh
 # Custom entrypoint for Kong that builds Lua expressions for request-transformer
 # and performs environment variable substitution in the declarative config.