Reduce build image components templates size

ImageBuilder has a limit of 16000. This commit reduces the size and add a unit test to prevent the template hitting the limit when parameters with long values are provided

Co-authored-by: Himani Anil Deshpande <himanidp@amazon.com>

Author: hanwen-cluster

cli/src/pcluster/config/imagebuilder_config.py

@@ -340,7 +340,7 @@ def __init__(self, config: ImageBuilderConfig):
 
     def _set_default(self, config: ImageBuilderConfig):
         dev_settings = config.dev_settings
-        self.region = "{{ build.AWSRegion.outputs.stdout }}"
+        self.region = get_region()
         self.nvidia = {"enabled": "yes"} if config.build.installation.nvidia_software.enabled else {"enabled": "no"}
         self.lustre = {"enabled": "yes"} if config.build.installation.lustre_client.enabled else {"enabled": "no"}
         self.is_official_ami_build = "false"