feat: add GitHub template (#68)

Author: sivchari

.github/ISSUE_TEMPLATE

@@ -0,0 +1,43 @@
+name: Go Conference 2023 Proposal
+description: Go Conference 2023のProposalです
+title: "[Session title]: "
+assignees:
+  - sivchari
+  - Hiroya3
+body:
+  - type: input
+    id: speaker
+    attributes:
+      label: Speaker
+      placeholder: Gopher
+    validations:
+      required: true
+
+  - type: textarea
+    id: account
+    attributes:
+      label: SNS Accounts
+      placeholder: [Twitter](https://twitter.com/goconjp)
+    validations:
+      required: false
+
+  - type: textarea
+    id: description
+    attributes:
+      label: Description
+      placeholder: What's new in Go1.20 ?
+    validations:
+      required: true
+
+  - type: dropdown
+    id: type
+    attributes:
+      label: Session type
+      options:
+        - LT(5min)
+        - Short Talk(20min)
+        - Challenge Session(20min)
+        - Long Talk(40min)
+    validations:
+      required: true
+