Add issue and PR templates (#277)

Author: benjie

.github/ISSUE_TEMPLATE/action-item.md

@@ -0,0 +1,16 @@
+---
+name: Meeting Action Item
+about:
+  Template for action items recommended during GraphQL-over-HTTP WG meetings.
+labels: "Action item :clapper:"
+---
+
+<!-- description -->
+
+- assignee(s): <!-- @mention, @mention -->
+- source: <!-- link to meeting notes -->
+
+---
+
+_Note: Action Item issues are reviewed and closed during Working Group
+meetings._

.github/PULL_REQUEST_TEMPLATE/agenda-attendance.md

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+---
+name: Meeting Agenda or Attendance
+about:
+  Template for adding agenda or attendance to an upcoming GraphQL-over-HTTP WG
+  meeting.
+labels: "Agenda :hand:"
+---
+
+<!--
+
+Before attending a GraphQL Working Group meeting, please check the following:
+
+- You (or your organization) has signed the Specification Membership Agreement.
+  https://github.com/graphql/foundation
+
+- You have read the participation guidelines and intend on contributing to the discussion. To respect meeting size, attendees should be relevant to the agenda. Recordings and notes will be posted after the meeting.
+  https://github.com/graphql/graphql-wg#participation-guidelines
+
+- Agenda items must include:
+  - Relevant links (RFC, issues, PRs)
+  - Champion's name
+  - Expected time to discuss
+
+-->