config: updates iceberg property description

[Deflaimun]

Updates iceberg_enable cluster property with documentation suggestions.
Introduced on #23443

Backports Required

• none - not a bug fix
• none - this is a backport
• none - issue does not exist in previous branches
• none - papercut/not impactful enough to backport
• v24.2.x
• v24.1.x
• v23.3.x

Release Notes

• none

[bharathv]

This enables it at the cluster level

This gives an impression that the cluster level default is set to true, should we reword it to say that this only enables the feature and the default for all topics is still false?

[micheleRP]

Thanks @bharathv. How is this:

Enables the feature that translates topic data to Iceberg tables. When set to true, this enables the feature at the cluster level and requires individual topics to explicitly opt in by setting the iceberg.enabled topic-level property to true. When set to false, this disables the feature at the cluster level, effectively turning it off for all topics.

[bharathv]

lgtm.

[vbotbuildovich]

ducktape was retried in https://buildkite.com/redpanda/redpanda/builds/55496#0192457e-b42e-4ba1-8b7a-0bb089cb0e1c

ducktape was retried in https://buildkite.com/redpanda/redpanda/builds/55496#0192457e-b434-4777-880e-539ab24f7453

ducktape was retried in https://buildkite.com/redpanda/redpanda/builds/55543#019248b3-051e-46a4-b3f9-79dea70a3750

[Deflaimun]

Updated the PR with the latest suggestion.

[micheleRP]

lgtm, thanks Paulo!

[vbotbuildovich]

new failures in https://buildkite.com/redpanda/redpanda/builds/55543#019248c0-de55-4e7b-8166-7b9ec251d28d:

"rptest.tests.read_replica_e2e_test.TestReadReplicaService.test_writes_forbidden.partition_count=10.cloud_storage_type=CloudStorageType.ABS"