Add GitHub templates for epics, bugs and release PRs (neondatabase/cloud#2079)

After merging this we will be able to:
- Pick Epic or Bug template in the GitHub UI, when creating an issue
- Use this link to open a release PR formatted in a unified way and
  containing a checklist with useful links: https://github.com/neondatabase/neon/compare/release...main?template=release-pr.md&title=Release%20202Y-MM-DD

.github/ISSUE_TEMPLATE/bug-template.md

@@ -0,0 +1,23 @@
+---
+name: Bug Template
+about: Used for describing bugs
+title: ''
+labels: t/bug
+assignees: ''
+
+---
+
+## Steps to reproduce
+
+
+## Expected result
+
+
+## Actual result
+
+
+## Environment
+
+
+## Logs, links
+- 

.github/ISSUE_TEMPLATE/epic-template.md

@@ -0,0 +1,25 @@
+---
+name: Epic Template
+about: A set of related tasks contributing towards specific outcome, comprizing of
+  more than 1 week of work.
+title: 'Epic: '
+labels: t/Epic
+assignees: ''
+
+---
+
+## Motivation
+
+
+## DoD
+
+
+## Implementation ideas
+
+
+## Tasks
+- [ ]
+
+
+## Other related tasks and Epics
+- 

.github/PULL_REQUEST_TEMPLATE/release-pr.md

@@ -0,0 +1,20 @@
+## Release 202Y-MM-DD
+
+**NB: this PR must be merged only by 'Create a merge commit'!**
+
+### Checklist when preparing for release
+- [ ] Read or refresh [the release flow guide](https://github.com/neondatabase/cloud/wiki/Release:-general-flow)
+- [ ] Ask in the [cloud Slack channel](https://neondb.slack.com/archives/C033A2WE6BZ) that you are going to rollout the release. Any blockers?
+- [ ] Does this release contain any db migrations? Destructive ones? What is the rollback plan?
+
+<!-- List everything that should be done **before** release, any issues / setting changes / etc -->
+
+### Checklist after release
+- [ ] Based on the merged commits write release notes and open a PR into `website` repo ([example](https://github.com/neondatabase/website/pull/120/files))
+- [ ] Check [#dev-production-stream](https://neondb.slack.com/archives/C03F5SM1N02) Slack channel
+- [ ] Check [stuck projects page](https://console.neon.tech/admin/projects?sort=last_active&order=desc&stuck=true)
+- [ ] Check [recent operation failures](https://console.neon.tech/admin/operations?action=create_timeline%2Cstart_compute%2Cstop_compute%2Csuspend_compute%2Capply_config%2Cdelete_timeline%2Cdelete_tenant%2Ccreate_branch%2Ccheck_availability&sort=updated_at&order=desc&had_retries=some)
+- [ ] Check [cloud SLO dashboard](https://observer.zenith.tech/d/_oWcBMJ7k/cloud-slos?orgId=1)
+- [ ] Check [compute startup metrics dashboard](https://observer.zenith.tech/d/5OkYJEmVz/compute-startup-time)
+
+<!-- List everything that should be done **after** release, any admin UI configuration / Grafana dashboard / alert changes / setting changes / etc -->