Adding the ability to force ttl to be constant

What I intended earlier was something like this:

```java
public class ConfigTtlProvider implements TenantTtlProvider {
    private static final boolean ARE_TTLS_FORCED = Configuration.getInstance().getBooleanProperty(TtlConfig.ARE_TTLS_FORCED);

    public boolean areTTLsForced() {
        return ARE_TTLS_FORCED;
    }
}
```

It should be treated as a constant and not looked up every time.

The other approach would be to consult the config in `forceTTLsIfConfigured(...)` and use those supplied values, rather than store/lookup them in this class. That still incurs a lot of essentially needless map lookups though. I like the idea of caching it once and using the cached value everywhere.

The same thing applies for the value returned by `getConfigTTLForIngestion()`. It is essentially a constant as well.