Adds auth support for Redis 6

[asyrique]

This PR contains the following changes:

• Adds the username optional key to the IRedisOptions interface and instantiation options.
• Adds 2 extra error handlers for handling Redis 6 default user not needing password and user passing username and password to a Redis <=5 instance (https://github.com/luin/ioredis/pull/1130/files#diff-43fd638f7be3d3664e2c4ee36dbdf059R32-R50)
• Update URL parser to handle for username passed in redis URL
• Tests for redis 5 and redis 6 using the new auth code.

Fixes #1097

[asyrique]

@luin This should be ready to be reviewed.
I didn't know whether this merited a patch version bump or a minor version bump, so defer to you on that.

Let me know if there's anything I need to fix in this PR.

[asyrique]

@luin Is there anything I can change / help to do that can help get this merged? I think I've covered all of the cases in the tests I wrote, but if there's a test case I missed out, if you can describe the case, I can write a test for it.

Thanks and appreciate all the work you do to keep this library fast and secure!

[luin]

Sorry for the late response. Code-wise it looks good to me 👍, just left two comments. I'll test thoroughly and merge the PR this weekend.

[ioredis-robot]

🎉 This PR is included in version 4.17.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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