docs(example): move config.yaml to config folder (#265)

ref: https://github.com/TwiN/gatus/issues/151#issuecomment-912932934

update all exmaple in docker-compose file.

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

.examples/docker-compose-grafana-prometheus/config/config.yaml

@@ -0,0 +1,16 @@
+metrics: true
+endpoints:
+  - name: website
+    url: https://twin.sh/health
+    interval: 30s
+    conditions:
+      - "[STATUS] == 200"
+  - name: github
+    url: https://api.github.com/healthz
+    interval: 5m
+    conditions:
+      - "[STATUS] == 200"
+  - name: example
+    url: https://example.com/
+    conditions:
+      - "[STATUS] == 200"