[build] Use Node.js v20 engine as minimum version

The reasons:
- The mainenance of Node.js v18 (LTS) ends 2025-04-30, so it's time to update the engine
- A lot of used dependencies declare Node.js v20 as minimum version,
it doesn't make sence to continue using v18 as minimum Node.js engine version, f.i.:

```
npm WARN EBADENGINE Unsupported engine {
npm WARN EBADENGINE   package: 'glob@11.0.1',
npm WARN EBADENGINE   required: { node: '20 || >=22' },
npm WARN EBADENGINE   current: { node: 'v18.17.1', npm: '9.6.7' }
npm WARN EBADENGINE }
...
npm WARN EBADENGINE Unsupported engine {
npm WARN EBADENGINE   package: 'path-scurry@2.0.0',
npm WARN EBADENGINE   required: { node: '20 || >=22' },
npm WARN EBADENGINE   current: { node: 'v18.17.1', npm: '9.6.7' }
npm WARN EBADENGINE }
...
npm WARN EBADENGINE Unsupported engine {
npm WARN EBADENGINE   package: 'lru-cache@11.0.0',
npm WARN EBADENGINE   required: { node: '20 || >=22' },
npm WARN EBADENGINE   current: { node: 'v18.17.1', npm: '9.6.7' }
npm WARN EBADENGINE }
```

Signed-off-by: Victor Rubezhny <vrubezhny@redhat.com>

Author: vrubezhny

CONTRIBUTING.md

@@ -8,7 +8,7 @@ There are only a few guidelines that we need contributors to follow.
 ## First Time Setup
 1. Install prerequisites:
    * latest [Visual Studio Code](https://code.visualstudio.com/)
-   * [Node.js](https://nodejs.org/) v18.17.0 or higher
+   * [Node.js](https://nodejs.org/) v20 or higher
      * It is recommended to set up `nvm` to manage different versions of node, which can be installed by following the instructions [here](https://github.com/nvm-sh/nvm#installing-and-updating).
      * To use the current recommended version for this project (in`./nvmrc`), run `nvm use`.
    * [Red Hat Authentication](https://marketplace.visualstudio.com/items?itemName=redhat.vscode-redhat-account) VS Code plugin (VS Code will prompt to install this when you launch the extension if you don't have it)

package-lock.json

@@ -14,8 +14,8 @@
 	"bugs": "https://github.com/redhat-developer/vscode-openshift-tools/issues",
 	"engines": {
 		"vscode": "^1.82.3",
-		"npm": ">=8.6.0",
-		"node": ">=18.0.0"
+		"npm": ">=9.6.4",
+		"node": ">=20.0.0"
 	},
 	"badges": [
 		{
@@ -100,7 +100,7 @@
 		"@types/git-url-parse": "^9.0.3",
 		"@types/lodash": "^4.17.16",
 		"@types/mocha": "^10.0.10",
-		"@types/node": "^18.19.85",
+		"@types/node": "^20.14.8",
 		"@types/proxyquire": "^1.3.31",
 		"@types/react": "^18.3.20",
 		"@types/react-copy-to-clipboard": "^5.0.7",