fix(90% utilization): Use simulated racks

[yarongilor]

Added a usage of simulated_racks to the 90%-utilizations tests of nemesis and of many-small-tables.

Testing

• elasticity-90-percent-with-nemesis-simulate-rack
• scale-elasticity-many-small-tables-simulated-rack

PR pre-checks (self review)

• I added the relevant backport labels
• I didn't leave commented-out/debugging code

Reminders

• Add New configuration option and document them (in sdcm/sct_config.py)
• Add unit tests to cover my changes (under unit-test/ folder)
• Update the Readme/doc folder relevant to this change (if needed)

[yarongilor]

The log shows the simulated racks like:

< t:2025-03-04 09:22:01,178 f:base.py         l:231  c:RemoteLibSSH2CmdRunner p:DEBUG > <10.4.3.151>: -- Address    Load      Tokens Owns Host ID                              Rack 
< t:2025-03-04 09:22:01,178 f:base.py         l:231  c:RemoteLibSSH2CmdRunner p:DEBUG > <10.4.3.151>: UN 10.4.0.154 ?         256    ?    5da7b762-32a5-4970-ab74-704465403fbc RACK2
< t:2025-03-04 09:22:01,178 f:base.py         l:231  c:RemoteLibSSH2CmdRunner p:DEBUG > <10.4.3.151>: UN 10.4.0.70  446.26 KB 256    ?    0ba190d2-cae1-42cd-a75d-585785d4075d RACK0
< t:2025-03-04 09:22:01,178 f:base.py         l:231  c:RemoteLibSSH2CmdRunner p:DEBUG > <10.4.3.151>: UN 10.4.3.151 486.68 KB 256    ?    de5a458e-9c64-4241-8a68-1a5b8da3ba09 RACK1