Add Gitpod config (#2000)

Hi @JanCizmar !

I wanted to help with setting up a Gitpod config. You can try it out by
opening this link:
https://gitpod.io/#https://github.com/tolgee/tolgee-platform/pull/2000
(use the **Large** 8-core machine for better performance)

And if you find it appropriate, could you add the following message at
the top of https://github.com/tolgee/tolgee-platform/wiki/Development ?
It could be helpful for contributors.

```markdown
## Getting Started with Gitpod

To quickly start, open this link: [https://gitpod.io/#github.com/tolgee/tolgee-platform](https://gitpod.io/#github.com/tolgee/tolgee-platform) to create a CDE for this repository.

A [CDE](https://www.gitpod.io/cde) will be created for you with your preferred editor (such as VSCode, Jetbrains, or SSH). All the necessary dependencies are automatically installed, and the tolgee-platform source code will be pre-built according to the [.gitpod.yml](/.gitpod.yml) file, this allows you to get started in just a few seconds.
```

.gitpod.yml

@@ -0,0 +1,69 @@
+# See https://www.gitpod.io/docs/introduction/languages/java
+
+image:
+  file: docker/gitpod.Dockerfile
+
+tasks:
+  - name: Build cache
+    openMode: tab-before
+    init: |
+      (
+        # Frontend cache
+        rm -f /workspace/.f
+        pushd webapp
+        npm ci
+        popd
+        touch /workspace/.f
+      ) &
+
+      # Backend cache
+      rm -f /workspace/.b
+      ./gradlew server-app:unpack
+      touch /workspace/.b
+
+  
+  - name: Backend
+    openMode: split-left
+    command: |
+      until test -e /workspace/.b; do sleep 1; done
+      ./gradlew server-app:bootRun --args='--spring.profiles.active=dev'
+
+  - name: Frontend
+    openMode: split-right
+    command: |
+      printf "\033[3J\033c\033[3J"
+
+      # Fix API server address for Gitpod VSCode Web
+      echo "REACT_APP_API_URL=$(gp url 8080)" > webapp/.env.local
+
+      until test -e /workspace/.f; do sleep 1; done
+      # Schedule auto-refresh for the webapp preview window after backend is fully up,
+      # as the webapp will probably have an error on the first render.
+      (
+        until curl -s -o /dev/null http://localhost:3000; do continue; done
+        echo "> GITPOD-INFO: Backend server might not be ready at port 8080 yet, expect error on webapp/frontend preview"
+        (while true; do sleep 1; echo -n .; done) &
+        gp ports await 8080 && kill $!
+        echo "> GITPOD-INFO: Refreshing webapp/frontend preview at port 3000"
+        gp preview "$(gp url 3000)"
+      ) &
+      cd webapp && BROWSER='' npm run start
+
+ports:
+  - name: Backend
+    port: 8080
+    visibility: public
+    onOpen: ignore
+
+  - name: Frontend
+    port: 3000
+    visibility: public
+    onOpen: open-preview
+
+  - port: 15000-50000
+    onOpen: ignore
+    description: Misc.
+
+vscode:
+  extensions:
+    - vscjava.vscode-java-pack

docker/gitpod.Dockerfile

@@ -0,0 +1,9 @@
+# Src: https://github.com/gitpod-io/workspace-images/tree/main/chunks/lang-java
+FROM gitpod/workspace-java-17@sha256:9afcbfd630163f00cab4bceab2d041e028c5b774019a40cb533f17d7ffa98350
+
+# Merge workspace-node image to workspace-java-17
+# Src: https://github.com/gitpod-io/workspace-images/tree/main/chunks/lang-node
+COPY --from=gitpod/workspace-node@sha256:08e175d076c1197774438c8a26cc978a9cde5f96795ccd0ebce0c2b6f5035170 / /
+ENV NODE_VERSION=21.2.0
+ENV PNPM_HOME=/home/gitpod/.pnpm
+ENV PATH=/home/gitpod/.nvm/versions/node/v${NODE_VERSION}/bin:/home/gitpod/.yarn/bin:${PNPM_HOME}:$PATH