fix: respect ctx in cmds run within DialContext

[mitchsw]

The DialContext() function does not use the new DoContext() methods (added in v1.8.6) when configuring auth/clientName/db during connection creation. If the Redis server is unresponsive, this can cause DialContext() to run for a very long time (instead of cancelling when the deadline is exceeded). DoContext should be used for these cmds.

Repro steps:

1. Make Redis unresponsive: CLIENT PAUSE 36000000 ALL
2. Attempt to DialContext() with a 1sec timeout
3. Command is unexpectedly blocked for a long time

[mitchsw]

Thanks @stevenh! Is it possible to please merge & tag this fix?

[stevenh]

To make sure you didn't miss it tag was done last week @mitchsw