support conditional config

**Describe the problem you have/What new integration you would like**

**Please describe your use case for this integration and alternatives you've tried:**

**Additional context**

it would be very nice and handy if some parts of config file could be variable based on the condition.
Example:
- my entire package of sensors has default logger level ERROR (so almost nothing on the screen)
- but for some sensors I would like to have DEBUG
- I am thinking this way:
```
logger: !if
condition: ${log_level}
then:
level: ${log_level}
else:
level: ERROR

```
so if log_leve is specified (i.e. DEBUG) my new level = DEBUG, otherwise it is ERROR