Support individual scrolls datasets (#1740)

* Support individual scrolls datasets

* Add qmsum context

* Fix formatting

lm_eval/tasks/scrolls/scrolls.yaml

-group: scrolls
-task:
-  - task: scrolls_qasper
-    class: !function task.Qasper
-  - task: scrolls_quality
-    class: !function task.QuALITY
-  - task: scrolls_narrativeqa
-    class: !function task.NarrativeQA
-  - task: scrolls_contractnli
-    class: !function task.ContractNLI
-  - task: scrolls_govreport
-    class: !function task.GovReport
-  - task: scrolls_summscreenfd
-    class: !function task.SummScreenFD
-  - task: scrolls_qmsum
-    class: !function task.QMSum

lm_eval/tasks/scrolls/scrolls_contractnli.yaml

+group: scrolls
+task: scrolls_contractnli
+class: !function task.ContractNLI

lm_eval/tasks/scrolls/scrolls_govreport.yaml

+group: scrolls
+task: scrolls_govreport
+class: !function task.GovReport

lm_eval/tasks/scrolls/scrolls_narrativeqa.yaml

+group: scrolls
+task: scrolls_narrativeqa
+class: !function task.NarrativeQA

lm_eval/tasks/scrolls/scrolls_qasper.yaml

+group: scrolls
+task: scrolls_qasper
+class: !function task.Qasper

lm_eval/tasks/scrolls/scrolls_qmsum.yaml

+group: scrolls
+task: scrolls_qmsum
+class: !function task.QMSum

lm_eval/tasks/scrolls/scrolls_quality.yaml

+group: scrolls
+task: scrolls_quality
+class: !function task.QuALITY

lm_eval/tasks/scrolls/scrolls_summscreenfd.yaml

+group: scrolls
+task: scrolls_summscreenfd
+class: !function task.SummScreenFD