chore(dockerfile): move to distroless (#2885)

* chore(dockerfile): move to distroless
- remove unnecessary env vars (these are provided via the deployment system)
- uses relative paths if in a working directory

* Amend entrypoint for use with distroless

* Update startup probe & docker compose readiness probe

docker-compose-speckle.yml

@@ -39,7 +39,7 @@ services:
     healthcheck:
       test:
         - CMD
-        - node
+        - /nodejs/bin/node
         - -e
         - "try { require('node:http').request({headers: {'Content-Type': 'application/json'}, port:3000, hostname:'127.0.0.1', path:'/readiness', method: 'GET', timeout: 2000 }, (res) => { body = ''; res.on('data', (chunk) => {body += chunk;}); res.on('end', () => {process.exit(res.statusCode != 200 || body.toLowerCase().includes('error'));}); }).end(); } catch { process.exit(1); }"
       interval: 10s