Added `--stream-prefix` option for `get` command

[ajenkinski]

Added a --stream-prefix (-p for short) option to awslogs get, to tell it to treat the log_stream_name argument as a name prefix instead as a regular expression. This allows it to delegate the log stream filtering to AWS, which avoids performance problems and throttling errors for log groups with large numbers of streams. The problem this fixes is described in #358.

Fixes #358

[p0wl]

would be great to get this merged! wdyt @jorgebastida ?

[sidpremkumar]

Any chance we would merge this?