[Feature] add datasets in unified format

[zqwerty]

Describe the feature Transform the following datasets into the Unified format under data/unified_datasets. Suggestions of adding/deleting datasets are welcome!

• [x] MultiWOZ 2.1
• [ ] MultiWOZ 2.2
• [ ] MultiWOZ 2.0
• [ ] MultiWOZ 2.3
• [ ] MultiWOZ 2.4
• [x] Schema-Guided Dialog
• [x] Taskmaster-1
• [x] Taskmaster-2
• [x] Taskmaster-3
• [x] MetaLWOZ
• [x] CrossWOZ
• [ ] Frames
• [x] WOZ 2.0
• [x] CamRest
• [ ] MSR-E2E
• [x] KVRET
• [ ] GSIM
• [ ] DSTC2
• [ ] ABCD
• [ ] MultiDoGo
• [ ] ATIS
• [ ] SNIPS
• [ ] CLINC
• [ ] Banking
• [ ] HWU
• [ ] Restaurant8k
• [ ] TOP
• [ ] MIT movie
• [ ] MIT restaurant
• [ ] E2E NLG
• [ ] RNNLG
• [ ] Facebook en
• [ ] STAR
• [ ] smcalflow
• [ ] TreeDST
• [ ] SLURP

Expected behavior Unified datasets can support related tasks.