encourage adding 👍 to express interest

decided on the @NixOS/documentation-team, see NixOS/nix.dev#359 for more information

.github/ISSUE_TEMPLATE/bug_report.md

@@ -30,3 +30,7 @@ A clear and concise description of what you expected to happen.
 **Additional context**
 
 Add any other context about the problem here.
+
+**Priorities**
+
+Add :+1: to [issues you find important](https://github.com/NixOS/nix/issues?q=is%3Aissue+is%3Aopen+sort%3Areactions-%2B1-desc).

.github/ISSUE_TEMPLATE/feature_request.md

@@ -18,3 +18,7 @@ A clear and concise description of any alternative solutions or features you've
 
 **Additional context**
 Add any other context or screenshots about the feature request here.
+
+**Priorities**
+
+Add :+1: to [issues you find important](https://github.com/NixOS/nix/issues?q=is%3Aissue+is%3Aopen+sort%3Areactions-%2B1-desc).

.github/ISSUE_TEMPLATE/missing_documentation.md

@@ -26,3 +26,6 @@ assignees: ''
 
 <!-- propose a solution -->
 
+## Priorities
+
+Add :+1: to [issues you find important](https://github.com/NixOS/nix/issues?q=is%3Aissue+is%3Aopen+sort%3Areactions-%2B1-desc).

.github/PULL_REQUEST_TEMPLATE/pull_request_template.md

@@ -5,3 +5,7 @@ Please include relevant [release notes](https://github.com/NixOS/nix/blob/master
 **Testing**
 
 If this issue is a regression or something that should block release, please consider including a test either in the [testsuite](https://github.com/NixOS/nix/tree/master/tests) or as a [hydraJob]( https://github.com/NixOS/nix/blob/master/flake.nix#L396) so that it can be part of the [automatic checks](https://hydra.nixos.org/jobset/nix/master).
+
+**Priorities**
+
+Add :+1: to [pull requests you find important](https://github.com/NixOS/nix/pulls?q=is%3Aopen+sort%3Areactions-%2B1-desc).