feature request: allow to define initial ChangeAgeLimit

[hartmut-co-uk]

As a connect user/admin I'd like to be able to configure scylla.change.age.limit.

(quoting scylla-cdc-go)

When the library starts for the first time it has to start consuming changes from some point in time. This parameter defines how far in the past it needs to look. If the value of the parameter is set to an hour, then the library will only read historical changes that are no older than an hour.

Consuming from a 'connector::table::vnodeId::streamId' should start from ~
max(persistedState, now()-tableCdcTtl, now()-changeAgeLimit)

References

• https://github.com/scylladb/scylla-cdc-go/blob/master/reader.go#L123-L135
• Infer ChangeAgeLimit from the TTL property of the CDC table scylla-cdc-go#9