Migrate signal_workflow_test to parallelsuite

[long-nt-tran]

What changed?

As titled.

Changes are:

• suite is now a self-referencing embedded parallelsuite.Suite[...]
• each test gets their own env := testcore.NewEnv(s.T()). Note that tests that overrides env.OverrideDynamicConfig(dynamicconfig.EnableCrossNamespaceCommands, true) needs their own dedicated cluster in the new (parallel) suite because they override a global setting, so those ones creates the new testEnv with testcore.WithDedicatedCluster() option
• s. -> env. for env-provided APIs (basically comms to test temporal cluster, etc...)
• testcore.NewContext() -> env.Context() to use test-level ctx from the env we created

Why?

Migrating to a better framework and enabling parallel test runs.

How did you test it?

• built
• run locally and tested manually
• covered by existing tests
• added new unit test(s)
• added new functional test(s)

Before

$ go test ./tests/ -run 'TestSignalWorkflowTestSuite' -count=1
ok      go.temporal.io/server/tests     59.685s

After

$ go test ./tests/ -run 'TestSignalWorkflowTestSuite' -count=1
ok      go.temporal.io/server/tests     11.557s