added announcement template (#1931)

.github/ISSUE_TEMPLATE/announcement.md

@@ -0,0 +1,34 @@
+---
+name: Announcement
+about: Submit an announcement
+title: ''
+labels: Announcement
+assignees: ''
+
+---
+
+**Breaking changes**
+<!-- Short description of the upcoming change -->
+
+**Target date**
+<!-- Date of changes propagation start -->
+
+**The motivation for the changes**
+<!-- Description of main reasons for this change -->
+
+**Possible impact**
+<!-- Description of who might be impacted by this change -->
+
+**Virtual environments affected**
+- [ ] Ubuntu 16.04
+- [ ] Ubuntu 18.04
+- [ ] Ubuntu 20.04
+- [ ] macOS 10.13
+- [ ] macOS 10.14
+- [ ] macOS 10.15
+- [ ] macOS 11.0
+- [ ] Windows Server 2016 R2
+- [ ] Windows Server 2019
+
+**Mitigation ways**
+<!-- Steps or options for impact mitigation -->