[Feature request] Enable player login

[dtest]

Add endpoints for players to login and logout

New endpoints for authentication server and players service:

• PUT /players/login: takes username and password as arguments. Returns playerUUID on success
• PUT /players/logout: takes playerUUID as argument, returns 200 success, but no content (some concerns about authenticating access to this endpoint, but really no endpoint should be able to be hit without proper credentials)

This will update a 'logged_in' timestamp field in the players table, which will be set to null on logout.

Track login events in a separate table player_login_entries

[dtest]

To do login, we need a way for generated players/bots to know the password.

Currently the load generators generate a random password. This logic can be changed to be a deterministic password, since these are not real players.

[dtest]

The login tracking will be handled through issue #34