MINOR: spoe: Add 'option continue-on-error' statement in spoe-agent section

MINOR: spoe: Add 'option continue-on-error' statement in spoe-agent section

By default, for a specific stream, when an abnormal/unexpected error occurs, the
SPOE is disabled for all the transaction. So if you have several events
configured, such error on an event will disabled all followings. For TCP
streams, this will disable the SPOE for the whole session. For HTTP streams,
this will disable it for the transaction (request and response).

To bypass this behaviour, you can set 'continue-on-error' option in 'spoe-agent'
section. With this option, only the current event will be ignored.