add mmlu tasks from pile-t5 (#1710)

* add mmlu tasks from pile-t5

* Update _mmlu_flan_cot_fewshot_template_yaml

* Update _mmlu_flan_cot_zeroshot_template_yaml

* Update _mmlu_flan_generative_template_yaml

* Update _mmlu_flan_loglikelihood_template_yaml

* Update _default_template_yaml

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Co-authored-by: Hailey Schoelkopf <65563625+haileyschoelkopf@users.noreply.github.com>

lm_eval/tasks/mmlu/generative/mmlu_us_foreign_policy.yaml

+"dataset_name": "us_foreign_policy"
+"description": "The following are multiple choice questions (with answers) about us\
+  \ foreign policy.\n\n"
+"group": "mmlu_social_sciences_generative"
+"group_alias": "social_sciences"
+"include": "_default_template_yaml"
+"task": "mmlu_us_foreign_policy_generative"
+"task_alias": "us_foreign_policy"

lm_eval/tasks/mmlu/generative/mmlu_virology.yaml

+"dataset_name": "virology"
+"description": "The following are multiple choice questions (with answers) about virology.\n\
+  \n"
+"group": "mmlu_other_generative"
+"group_alias": "other"
+"include": "_default_template_yaml"
+"task": "mmlu_virology_generative"
+"task_alias": "virology"

lm_eval/tasks/mmlu/generative/mmlu_world_religions.yaml

+"dataset_name": "world_religions"
+"description": "The following are multiple choice questions (with answers) about world\
+  \ religions.\n\n"
+"group": "mmlu_humanities_generative"
+"group_alias": "humanities"
+"include": "_default_template_yaml"
+"task": "mmlu_world_religions_generative"
+"task_alias": "world_religions"