Add Changesets configuration and update development documentation (#1964)

Introduce Changesets for versioning and changelog generation, and
enhance development documentation to guide contributors on using
Changesets effectively.

CONTRIBUTING.md

@@ -0,0 +1,54 @@
+# Plugin development
+
+## Building plugin
+
+```sh
+# install frontend deps
+yarn install --pure-lockfile
+# build frontend
+yarn build
+#build backend for current platform
+mage -v build:backend
+```
+
+## Rebuild backend on changes
+
+```sh
+mage watch
+```
+
+## Debugging backend plugin
+
+For debugging backend part written on Go, you should go through a few steps. First, build a plugin with special flags for debugging:
+
+```sh
+make build-debug
+```
+
+Then, configure your editor to connect to [delve](https://github.com/go-delve/delve) debugger running in headless mode. This is an example for VS Code:
+
+```json
+{
+  "version": "0.2.0",
+  "configurations": [
+    {
+      "name": "Debug backend plugin",
+      "type": "go",
+      "request": "attach",
+      "mode": "remote",
+      "port": 3222,
+      "host": "127.0.0.1"
+    }
+  ]
+}
+```
+
+Finally, run grafana-server and then execute `./debug-backend.sh` from grafana-zabbix root folder. This script will attach delve to running plugin. Now you can go to the VS Code and run _Debug backend plugin_ debug config.
+
+## Submitting PR
+
+If you are creating a PR, ensure to run `yarn changeset` from your branch. Provide the details accordingly. It will create `*.md` file inside `./.changeset` folder. Later during the release, based on these changesets, package version will be bumped and changelog will be generated.
+
+## Releasing & Bumping version
+
+To create a new release, execute `yarn changeset version`. This will update the Changelog and bump the version in `package.json` file. Commit those changes. Run the `Plugins - CD` GitHub Action to publish the new release.