chores: reduce amount of reconciles, cache CH connections between reconciles

[GrigoryPervakov]

Why

In transient states, the operator does a lot of reconciling, generating useless load on the apiserver and constantly reconnect all nodes.

What

• Increase most reconcile requests 1s->5s
• Add a ClickHouse connections pool

[Copilot]

Pull request overview

This PR reduces unnecessary reconcile churn in transient states and avoids repeatedly reconnecting to ClickHouse nodes by (1) slowing down common poll/requeue loops and (2) introducing a per-cluster ClickHouse connection cache that survives across reconciles and is cleaned up on manager shutdown.

Changes:

• Introduce a per-ClickHouseCluster connection pool (connCache) and wire it through the ClickHouse controller/commander, including shutdown cleanup.
• Increase several requeue/poll intervals from 1s to 5s by adding RequeueProbePoll and using it in multiple “wait/poll” paths.
• Update integration tests to use the new dialer + connection cache flow.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
internal/controller/resourcemanager.go	Switch replica-resource requeues to RequeueProbePoll to reduce apiserver churn.
internal/controller/keeper/sync.go	Slow down requeueing when cluster is not stable / waiting on replica readiness.
internal/controller/constants.go	Add RequeueProbePoll = 5s constant.
internal/controller/clickhouse/sync.go	Wire connection cache into commander creation; use RequeueProbePoll for blocked/requeue steps.
internal/controller/clickhouse/controller.go	Create/own the connection cache, evict on cluster deletion, and close on manager shutdown.
internal/controller/clickhouse/conncache.go	New per-cluster connection cache implementation with credential-hash invalidation.
internal/controller/clickhouse/commands.go	Commander now uses cached connections rather than per-reconcile connection maps.
internal/controller/clickhouse/commands_test.go	Adapt integration test to use dialer routing and cached connections.

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[mintlify]

Docs PR opened: ClickHouse/mintlify-docs-dev#247

Synced upstream clickhouse-operator docs, adding JBOD storage docs, a new CABundleSelector type, and server-side kubectl apply instructions.