The /proc/1/cgroup check to set the server_hostname when

running under docker is not working in all cases. We verified this by
exec-ing into our running container and checking the proc file contents:

```
❯ docker exec -it our-container sh # on host
$ cat /proc/1/cgroup # in container
0::/
```

This change introduced a a `VITESS_HOST` variable similarly to the
`MYSQL_HOST` variable used for standard MySQL connections. I've left the
original fallback in this case in case anything else was relying on it.
Our use case only calls for connecting to VITESS, but I suspect other DB
types could suffer from the same issue.

GitOrigin-RevId: 83d56771222b1a8601fcd4e8cb3b3849dbebe2ce

Author: mpeyper

misk-jdbc/src/main/kotlin/misk/jdbc/DataSourceConfig.kt

@@ -168,7 +168,7 @@ data class DataSourceConfig @JvmOverloads constructor(
       DataSourceType.VITESS_MYSQL -> {
         copy(
           port = port ?: 27003,
-          host = host ?: server_hostname,
+          host = host ?: System.getenv("VITESS_HOST") ?: server_hostname,
           database = database ?: "@master"
         )
       }