User-defined log stream prefix

[bartpio]

In the prior state, a user-defined log stream suffix may be provided, but the prefix is always of the form yyyy/mm/dd. In some usage scenarios, this can prevent efficient filtering of log streams when enumerating the streams in a group.

Allow an optional LogStreamNamePrefix configuration, which if specified, is used as the first segment of the prefix. If this configuration is engaged, the yyyy/mm/dd system-generated form will be used as the second segment of the prefix. The design invariant that a unique date-based segment is included in the stream name is maintained.

If the LogStreamNamePrefix configuration is not engaged, behavior will match the prior state; log stream names will begin with the yyyy/mm/dd segment.

[klaytaybai]

Thanks for bringing some attention to this and working on the PR. I'm assuming that you're aware of #1.

[normj]

Closing this and we will use your PR to track this feature request #84