Deprecate leader balancer mode

[ztlpn]

"Greedy" strategy is an older strategy that was left as an option in case there were issues with the newer topic-aware "random" strategy. Random strategy has been the default for several releases, so it doesn't make sense to keep the greedy strategy any more.

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

Improvements

• Deprecate leader_balancer_mode cluster config property.

[dotnwat]

src/v/cluster/tests/leader_balancer_test.cc:20:10: error: module //src/v/cluster/tests:leader_balancer_test does not depend on a module exporting 'utils/to_string.h'
--
  | 20 \| #include "utils/to_string.h"
  | \|          ^
  | 1 error generated.

[vbotbuildovich]

ducktape was retried in https://buildkite.com/redpanda/redpanda/builds/56491#01928cfd-296d-45e9-bcca-9c136a52105e
ducktape was retried in https://buildkite.com/redpanda/redpanda/builds/56491#01928d31-f10f-407c-a0ac-89666e4a4970

[vbotbuildovich]

Retry command for Build#56491

please wait until all jobs are finished before running the slash command

/ci-repeat 1
tests/rptest/tests/cloud_storage_timing_stress_test.py::CloudStorageTimingStressTest.test_cloud_storage@{"cleanup_policy":"delete"}

[ballard26]

LGTM