Add ReplicationConfigs to SessionConfig for excluding keyspaces from replica precompute

[michaelhly]

We add ReplicationOptions which includes a vector of keyspace names to SessionConfig. When instantiating ClusterData, we exclude keyspaces from provided by ReplicationOptions when computing PrecomputedReplicas to conserve memory/compute resources.

Fixes: #671

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• I added relevant tests for new features and bug fixes.
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[michaelhly]

@piodul @wprzytula @havaker would you mind taking a quick look? Happy to write tests and finish up docs if this looks like it's in the right track.

[piodul]

@Lorak-mmk please review

[Lorak-mmk]

You can already choose which keyspaces to precompute (see keyspaces_to_fetch) in SessionConfig, but:

• it is an allowlist, while your approach is denylist. I'm wondering if maybe the best approach is to allow both (make enum Allowlist(Vec) and Denylist(Vec) instead of just Vec).
• It prevents info about other keyspaces to be fetched at all (so it's not available in ClusterData), while your solution only avoids precomputing replication strategies.

So I think this change may be valuable. I'll try to post initial review soon.