Move observation_template from agent config into model configs

Author: john-b-yang

configs/mini/default.yaml

@@ -102,4 +102,3 @@ instance_template: |
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 step_limit: 30
 cost_limit: 0
-observation_template: "[Step {{n_model_calls}}/{{step_limit}} used - {{step_limit - n_model_calls}} left]\n{% if output.exception_info %}<exception>{{output.exception_info}}</exception>\n{% endif %}<returncode>{{output.returncode}}</returncode>\n<output>\n{{output.output}}</output>"