roachtest: add startOpts.RoachprodOpts.SkipWaitForSQL

[srosenberg]

In [1], WaitForSQLReady was added immediately after roachprod.Start to ensure freshly started nodes are ready to serve (and authenticate) SQL sessions. This behavior is specific to roachtest; i.e., roachprod start remains unchanged. The reason for WaitForSQLReady is described in [2]. Essentially, part of the SQL subsystem is initialized asynchronously; session authentication isn't available until it's fully initialized.

Some roachtests, e.g., cluster-init, set SkipInit, effectively disabling automated cluster initialization. In that case, WaitForSQLReady is also skipped, since we can't place a definite upper bound on when SQL will eventually be ready. More recently, another roachtest, namely network/authentication was found to flake due to WaitForSQLReady [3]. While the test was made compatible with WaitForSQLReady, it's likely we will run into other examples in the future. Thus, we should add an opt-out via startOpts.RoachprodOpts.SkipWaitForSQL.

[1] #138109
[2] #137988
[3] #138806

Jira issue: CRDB-47618

[blathers-crl]

cc @cockroachdb/test-eng