Proposal: Change serf Log Messages from INFO to NOTICE

#### Feature Description

This is a proposal to change the serf logging such as `EventMemberLeave`, `EventMemberFailed`, `EventMemberJoin`, and `agent.client.memberlist.X` messages from INFO to NOTICE log level.

#### Use Case(s)

The consul agent logs, at INFO level, have a great deal of abundant information, on top of this, the amount of serf/gossip related logging is an immense amount of logging information, that, at times, dilute the logs to the point where its difficult to find meaningful data when troubleshooting an issue.

Due to the amount of logging messages from gossiping/serf, and at times, in big deployments, how many there can be, while they aren't debug level messaging, moving them down to a more detailed log level seems to make sense.

Start by locating the Consul agent logging paths for EventMemberLeave, EventMemberFailed, EventMemberJoin, and agent.client.memberlist.X. Review how these serf messages are assigned their current INFO level and determine the affected logging entry points. Done means the specified messages use NOTICE while retaining the intended distinction from DEBUG-level output.

Written by the indexing model from the issue text.