delay starting cron and worker until Mautic is installed

Currently cron and werker service immediately start running, but this makes no sense if Mautic isn't installed yet.

This PR adds a simple check to see if Mautic is installed, by checking if the config file exists, and if so if the the site_url is set. This corresponds with the check that Mautic does internally when booting up.

To test this PR:

build the apache image based in this PR

docker build -t mautic/mautic:5-apache --build-arg MAUTIC_VERSION=5.0.3 -f apache/Dockerfile .

go to the basic example dir
```
❯ cd examples/basic
```
start the basic example
```
❯ docker compose up -d
```

verify the output of the worker container

❯ docker compose logs mautic_worker -f --no-log-prefix
Mautic not installed, waiting to start workers
Mautic not installed, waiting to start workers
Mautic not installed, waiting to start workers
Mautic not installed, waiting to start workers
...

install Mautic via the UI or CLI UI go to http://localhost:8001

CLI


docker compose exec -u www-data -w /var/www/html mautic_web php ./bin/console mautic:install http://localhost:8001 -f --admin_email=admin@example.com --admin_password=mautic

verify the output of the worker container

❯ docker compose logs mautic_worker -f --no-log-prefix
...
2024-02-19 21:12:49,262 INFO Set uid to user 0 succeeded
2024-02-19 21:12:49,265 INFO supervisord started with pid 251
2024-02-19 21:12:50,272 INFO spawned: 'messenger-consume-email_00' with pid 252
2024-02-19 21:12:50,274 INFO spawned: 'messenger-consume-email_01' with pid 253
2024-02-19 21:12:50,278 INFO spawned: 'messenger-consume-failed_00' with pid 254
2024-02-19 21:12:50,280 INFO spawned: 'messenger-consume-failed_01' with pid 255
2024-02-19 21:12:50,283 INFO spawned: 'messenger-consume-hit_00' with pid 256
2024-02-19 21:12:50,286 INFO spawned: 'messenger-consume-hit_01' with pid 257
...

mautic / docker-mautic

delay starting cron and worker until Mautic is installed #264