subsystem-bench: Extract prometheus endpoint launching from regression test cases to use it only with cli runner

[AndreiEres]

We use an awkward false argument to not initialize a prometheus endpoint inside regression tests. Otherwise, each test will start an unconfigurable endpoint, causing errors because they will use the same port 9999.

polkadot-sdk/polkadot/node/network/availability-recovery/tests/availability-recovery-regression-bench.rs

Line 100 in 475e7a1

prepare_test(config.clone(), &mut state, TestDataAvailability::Read(options), false);

It's better to extract the endpoint launching outside the test, as we already do with valgrind and pyroscope. But we still use prometheus inside the tests.

polkadot-sdk/polkadot/node/subsystem-bench/src/cli/subsystem-bench.rs

Lines 108 to 121 in 475e7a1

	let is_valgrind_running = valgrind::is_valgrind_running();
	if !is_valgrind_running && self.cache_misses {
	return valgrind::relaunch_in_valgrind_mode()
	}
	let agent_running = if self.profile {
	let agent = PyroscopeAgent::builder(self.pyroscope_url.as_str(), "subsystem-bench")
	.backend(pprof_backend(PprofConfig::new().sample_rate(self.pyroscope_sample_rate)))
	.build()?;
	Some(agent.start()?)
	} else {
	None
	};

[gitofdeepanshu]

Can I take this?