docs: add PR templates for the new release process

.github/PULL_REQUEST_TEMPLATE/feature_branch_pr_template.md

@@ -0,0 +1,11 @@
+### Motivation
+
+What was the motivation for the changes in this PR?
+
+### Acceptance Criteria
+
+- Include here all things that this PR should solve
+
+### Checklist
+
+- [ ] If you are requesting a merge into `master`, confirm this code is production-ready and can be included in future releases as soon as it gets merged 

.github/PULL_REQUEST_TEMPLATE/release_candidate_pr_template.md

@@ -0,0 +1,8 @@
+# Changes
+
+Link here all the PRs that are included in this release candidate
+
+# Checklist
+
+- [ ] I've read and followed the release candidate process described in https://github.com/HathorNetwork/ops-tools/blob/master/docs/release-guides/hathor-core.md#release-candidate
+- [ ] I confirm this release candidate only includes production-ready changes

.github/PULL_REQUEST_TEMPLATE/release_pr_template.md

@@ -0,0 +1,12 @@
+# Changes
+
+Link here all the PRs that are included in this release
+
+# Release-candidates
+
+Link here the release-candidates that were deployed as part of this release
+
+# Checklist
+
+- [ ] I've read and followed the release process described in https://github.com/HathorNetwork/ops-tools/blob/master/docs/release-guides/hathor-core.md#stable-release
+- [ ] The QA process was run successfully during the tests of the corresponding release-candidate(s)

.github/pull_request_template.md

@@ -0,0 +1,5 @@
+Please go to the `Preview` tab and select the appropriate Pull Request template:
+
+* [Feature Branch](?expand=1&template=feature_branch_pr_template.md) - Use this PR template when you are merging a feature branch into `master`
+* [Release Candidate](?expand=1&template=release_candidate_pr_template.md) - Use this PR template when you are merging `master` into `release-candidate`
+* [Release](?expand=1&template=release_pr_template.md) - Use this PR template when you are merging `release-candidate` into `release`