add readOnly on failover opts

[smilad]

fixing issues :
#3277

adding ReadOnly for scenarios where you need to connect to read-only replicas is not supported in UniversalClient

by adding this I can connect to readOnly and Master separately

[ndyakov]

Hello @smilad, thank you for the contribution. Would you please add a test for the change that you are introducing in this PR?

[smilad]

@ndyakov :
Done

[ndyakov]

@smilad The test you added is skipped and won't be executed. Can we have a test that will be executed and validate the new option?

[smilad]

@ndyakov : it is because of your sentinel options
and pipelines have problems
the first test case also has this issue
but if run test on local it is ok

[ndyakov]

@smilad lets work together on making sure we can execute the desired test in CI. Looking at your change, having a test that tries to write to a read only client should result in an error. We can test for that? Also we can make sure we are connected to a replica. Correct?