Support global configuration of log rotation

Presently, each service's section needs to include its own stdout_logfile_maxbytes and stdout_logfile_backups.

In our deployments, we make use of

[include]
files = ...

to include individual service configurations into a master supervisor.conf for a given product. Several products make use of a subset of shared service implementations.

We find that the same log rotation configuration is acceptable for all of our services in a given product, but they need to vary between products. For some products, we wish to manage our own log rotation, while in others it's desirable to have supervisord manage log rotation. So, I wanted to configure log rotation globally in each product's supervisor.conf, but there are not settings for it.

It seems to me that many others might be in the same situation: either needing different rotation config between products that share service implementations or simply wanting to configure the same log rotation for all services globally.