Remove the "cacheTtlSeconds" configuration option for connectors

ModeShape 3.x and 4.x has a configuration setting: cacheTtlSeconds which can be configured on external sources which indicates that a particular node coming from an external source should be cached for a limited amount of time in the workspace cache.

The purpose of this setting is to essentially prevent the WorkspaceCache from caching an external node for too long in order to avoid stale data.

With MODE-2526 however, this will no longer make sense since the TTL setting is Infinispan-specific. Instead, this setting should be removed and a new one added cacheable:true|false which either enables or completely disables workspace caching for a particular document/connector.

This is likely more than appropriate, since:
a) the old setting was only there to prevent stale data - which the new one completely eliminates
b) if a connector desires any more specialized caching semantic, it can always implement its own custom logic and disable the default one