Allow configuring additional connection options

[kierate]

When using RabbitMQ with a load balancer in front of multiple nodes, the load balancer will close any connection that has not received messages (i.e. are considered inactive) after a certain period of time (e.g. 60 seconds). This issue can easily be solved (since php-amqplib v2.4.1) simply by providing the heartbeat and read_write_timeout options when constructing the connection object.

This PR essentially exposes those parameters, so they can be configured configured as part of Tail settings.

On top of heartbeat and read_write_timeout this PR also allows configuring keepalive, read_write_timeout and ssl_context_options (these are not necessary for enabling heartbeats, but are also just parameters to the AMQPStreamConnection constructor).

The Connection class now uses AMQPSSLConnection because:

• it extends AMQPStreamConnection (same as AMQPConnection)
• it provides default values for AMQPStreamConnection (so Tail does not need to care about backwards compatibility for the new settings)
• when ssl_context_options are not provided it does not use SSL (behaves the same as AMQPConnection previously did)
• when ssl_context_options are not provided it deals with creating the SSL context (so Tail doesn't have to)