Point people filing issues to discussions

We are not yet at the point where Moonwalk will be managed
through issues.  This changes the new issue workflow
to offer buttons pointing to GitHub discussions and/or Slack,
along with a template that repeats the advice from OAI#11 to open
a discussion instead of an issue.

I somewhat strengthened OAI#11's language with the criteria that
issues need to be things we can resolve by PRs in the short term.

.github/ISSUE_TEMPLATE/config.yml

@@ -0,0 +1,8 @@
+blank_issues_enabled: true
+contact_links:
+  - name: Have an idea for Moonwalk?
+    url: https://github.com/OAI/sig-moonwalk/discussions
+    about: Please open or join a discussion instead of an issue!
+  - name: Want to chat about Moonwalk?
+    url: https://communityinviter.com/apps/open-api/openapi
+    about: "Please join the #sig-moonwalk channel on our Slack!"

.github/issue_template.md

@@ -0,0 +1,16 @@
+---
+name: ''
+about: Consider opening a discussion instead...
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+<!--
+During this early phase of Moonwalk work, issues should be reserved for defining, discussing, and tracking *known work items* with PR-able actions.
+
+If you want to suggest ideas, please consider starting a discussion instead!
+
+https://github.com/OAI/sig-moonwalk/discussions
+-->