Add dev container configuration

.devcontainer/devcontainer.json

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+// For format details, see https://aka.ms/devcontainer.json. For config options, see the
+// README at: https://github.com/devcontainers/templates/tree/main/src/javascript-node
+{
+	"name": "Node.js",
+
+	"dockerComposeFile": "docker-compose.yml",
+	"service": "app",
+	"workspaceFolder": "/fancy-gatus",
+	"shutdownAction": "stopCompose",
+
+	// Use 'forwardPorts' to make a list of ports inside the container available locally.
+	"forwardPorts": [
+		5173
+	],
+
+	// Configure tool-specific properties.
+	"customizations": {
+		"vscode": {
+			"extensions": [
+				"svelte.svelte-vscode",
+				"dbaeumer.vscode-eslint",
+				"esbenp.prettier-vscode",
+				"eamodio.gitlens"
+			]
+		}
+	}
+}

.devcontainer/docker-compose.yml

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+services:
+  app:
+    image: mcr.microsoft.com/devcontainers/javascript-node:1-22-bookworm
+    volumes:
+      - ..:/fancy-gatus:cached
+    command: sleep infinity