Add .vscode profile for easier contributions (#536)

### Description of the change

This adds a `.vscode` folder with recommended extensions and some useful settings like unittest schema validation.
The `.vscode` folder is already helm ignored during packaging.

### Possible drawbacks

We would have to be careful about PR changes in that directory.

Reviewed-on: https://gitea.com/gitea/helm-chart/pulls/536
Co-authored-by: justusbunsi <sk.bunsenbrenner@gmail.com>
Co-committed-by: justusbunsi <sk.bunsenbrenner@gmail.com>

.vscode/extensions.json

@@ -0,0 +1,8 @@
+{
+    "recommendations": [
+        "yzhang.markdown-all-in-one",
+        "DavidAnson.vscode-markdownlint",
+        "Tim-Koehler.helm-intellisense",
+        "esbenp.prettier-vscode"
+    ]
+  }

.vscode/settings.json

@@ -0,0 +1,8 @@
+{
+    "yaml.schemas": {
+        "https://raw.githubusercontent.com/helm-unittest/helm-unittest/main/schema/helm-testsuite.json": [
+            "/unittests/**/*.yaml"
+        ]
+    },
+    "yaml.schemaStore.enable": true
+}

CONTRIBUTING.md

@@ -9,12 +9,7 @@ refactorings for easier maintainability or documentation improvements.
 - [`helm`](https://helm.sh/docs/intro/install/)
 - `make` is optional; you may call the commands directly
 
-When using Visual Studio Code as IDE, following plugins might be useful:
+When using Visual Studio Code as IDE, a [ready-to-use profile](.vscode/) is available.
-
-- [Markdown All in One](https://marketplace.visualstudio.com/items?itemName=yzhang.markdown-all-in-one)
-- [markdownlint](https://marketplace.visualstudio.com/items?itemName=DavidAnson.vscode-markdownlint)
-- [Helm Intellisense](https://marketplace.visualstudio.com/items?itemName=Tim-Koehler.helm-intellisense)
-- [Prettier - Code formatter](https://marketplace.visualstudio.com/items?itemName=esbenp.prettier-vscode)
 
 ## Documentation Requirements
 
@@ -61,7 +56,7 @@ $ helm plugin install https://github.com/helm-unittest/helm-unittest
 make unittests
 ```
 
-See [plugin documentation](https://github.com/helm-unittest/helm-unittest/blob/v0.3.3/DOCUMENT.md) for usage instructions.
+See [plugin documentation](https://github.com/helm-unittest/helm-unittest/blob/main/DOCUMENT.md) for usage instructions.
 
 ## Release process