CDRIVER-938 prohibit calling unsafe client setters with pooled clients

[kevinAlbs]

Summary

Update mongoc_client_set_ssl_opts and mongoc_client_set_ssl_stream_initiator to ignore a pooled mongoc_client_t and logs an error.

Motivation

Intended to prevent a user configuring connection options on a pooled client that likely behave unexpectedly:

mongoc_client_t *client = mongoc_client_pool_pop (pool); // Monitoring starts.
mongoc_client_set_ssl_opts (client, opts); // Connections already created for monitoring!
mongoc_client_pool_push (pool, client); // Pushes client back onto pool with different TLS options!

Other mongoc_client_set_* functions are not modified.

Changes to mongoc_client_set_* functions

mongoc_client_set_ssl_opts and mongoc_client_set_ssl_stream_initiator

• Changed in this PR to ignore a single-threaded client and log an error.

mongoc_client_set_sockettimeoutms

• Not changed. Already documented to support a pooled client.

mongoc_client_set_write_concern, mongoc_client_set_read_concern, and mongoc_client_set_read_prefs

• Not changed. Can be supported with CDRIVER-3537 fixed.

mongoc_client_set_apm_callbacks, mongoc_client_set_structured_log_opts, mongoc_client_set_error_api, mongoc_client_set_appname, mongoc_client_set_server_api

• Not changed. Already error when passed a pooled client.

[vector-of-bool]

LGTM