[FEATURE] Enable the use of sticky key-range reader

[yjshen]

We could support sub-stream parallelism by using the sticky key-range reader.

apache/pulsar#5928

[yjshen]

After throughout discussion with @codelipenghui, current sticky consumer lacks three main capabilities:

• to create a consumer with immutable key-range at start time.
• enable consumption without the need to ack messages.
• the subscription seems to be different from that created from admin.topics.createSubscription()

[codelipenghui]

@yjshen
I noticed @jiazhai add support for exposing subscription mode at the consumer side. So that we can create a consumer with a non-durable subscription, it's more like a reader.

And I forgot that the sticky consumer is supported, so to create a consumer with immutable key-range, we can use

client.newConsumer()
               .keySharedPolicy(KeySharedPolicy.stickyHashRange().ranges(Range.of(0, 10)))
              .subscribe();

So, looks the current problem is to enable consumption without the need to ack messages. I think we can add a flag at the consumer side to indicate that if the consumer can be blocked by un-ack messages or not. @sijie @jiazhai Please help to check if this is reasonable.

Or we can disable the un-ack message check when the consumer with a non-durable subscription?

[jianyun8023]

pr #58 has completed this function.