fix(featrues-testcases): disable manager on too small monitor nodes

[fruch]

those case doesn't need manager installed, and they are fine with having smaller monitor node, that manager (scylla) can't be installed on.

Testing

• no testing is needed

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 relevent to this change (if needed)