[Backport 6.2] fix(test-case): update 5000 tables test case configuration

[scylladbbot]

List of changes:

• Disable per-table metrics due to significant perf impact.
• Enable cluster health checks which work with this case just fine.
• Decrease the nemesis interval from 60 minutes to just 3 keeping in mind that health checks will take some time too.
• Reduce stress time for each of the 5000 commands. Having 20 minutes per cmd we will get about 1.5 days long test runs instead of the 2.5 days.
• Reduce number of loaders from 5 to 3 to use resources more efficiently. In current case the bottleneck is the RAM.

Note that this scenario hits following bug:

• https://github.com/scylladb/scylla-enterprise/issues/5093

If destroy_data_then_repair nemesis gets triggered aganst the setup of this scenario.

Testing

• scylla-staging/valerii/vp-scale-5000-tables-test#7

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)

• (cherry picked from commit 0c7fa60)

Parent PR: #9843