feat: add a devcontainer for easier development

This change adds a devcontainer that adds `cscli` so that someone can
easily run tests in this repository.

I verified this works by running the example test command in the
`README.md`:
```sh
cscli hubtest run dovecot-logs
INFO[26-02-2025 19:00:00] Running test 'dovecot-logs'                  
INFO[26-02-2025 19:00:03] Test 'dovecot-logs' passed successfully (387 assertions) 
───────────────────────
 Test           Result 
───────────────────────
 dovecot-logs   ✅     
───────────────────────
```

This change also adds a workflow to make sure the devcontainer can
build.

.devcontainer/Dockerfile

@@ -0,0 +1,13 @@
+FROM alpine:latest AS builder
+RUN wget -q -o /tmp/install-crowdsec-repositories.sh https://install.crowdsec.net \
+    && chmod +x /tmp/install-crowdsec-repositories.sh
+
+
+FROM mcr.microsoft.com/devcontainers/base:debian
+COPY --from=builder /tmp/install-crowdsec-repositories.sh /tmp/install-crowdsec-repositories.sh
+RUN sh -c /tmp/install-crowdsec-repositories.sh \
+    && apt-get update \
+    && apt-get install -y --no-install-recommends \
+        crowdsec \
+    && apt-get clean \
+    && rm -rf /var/lib/apt/lists/*

.devcontainer/devcontainer.json

@@ -0,0 +1,6 @@
+{
+	"name": "CrowdSec Hub",
+	"build": {
+		"dockerfile": "Dockerfile"
+	}
+}

.github/workflows/devcontainer.yml

@@ -0,0 +1,22 @@
+name: Build DevContainer
+on:
+  push:
+    branches:
+      - master
+    paths:
+      - .devcontainer/**
+  pull_request:
+    branches:
+      - master
+    paths:
+      - .devcontainer/**
+
+jobs: 
+  devcontainer-build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: checkout repo
+        uses: actions/checkout@v4
+
+      - name: Build devcontainer image
+        uses: devcontainers/[email protected]