Add parsing of multiple URLs for cluster mode in redis

[stephaniehingtgen]

What this PR does
This PR adds a new function, ParseClusterURLs, which takes an array of strings and turns it into the array of addresses used for redis in cluster mode along with configurations passed in.

How it works
It is very similar to the ParseURL function, except for this function loops through an array of URLs. It will get the username and password for the cluster as well as configurations sent in through the query parameters.

Since the connection to the cluster can only have one username and password, if it differs between URLs in the array, the function will fail. Additionally, if the schemes differ, it will fail. I did not implement checks on the query parameters differing. If we want this done, I definitely could do it, but with the defaults and the init function it starts getting a bit uglier to check for all of those. If the query parameters do differ, it will use the last one in the array.

Example of arrays that will succeed:

["redis://localhost:6378", "redis://localhost:6379"]
["rediss://localhost:6378", "rediss://localhost:6379"]
["redis://foo:bar@localhost:6378?read_timeout=1s", "redis://foo:bar@localhost:6379?read_timeout=2s"] // no checks on query parameters

Example of arrays that will fail:

["redis://localhost:6378", "localhost:6379"] // schemes differ
["redis://foo:bar@localhost:6378", "redis://foo@localhost:6379"] // passwords differ
["redis://foo:bar@localhost:6378", "redis://foo:hello@localhost:6379"] // passwords differ
["redis://foo:bar@localhost:6378", "redis://bar:hello@localhost:6379"] // usernames differ

[stephaniehingtgen]

closing in favor of #1924