Rebranding docs/install/

[zuiderkwast]

This PR does the bulk of renaming:

• Remove "redis" in CLI prompt "redis 127.0.0.1:6379>"
• Change "Redis" to "Valkey" using Perl regex Redis(?! compatibility| v?[1-7]| version| < [1-7]| OSS|\.[a-z]|\w)
• Replace filenames redis(-cli|-server|-benchmark|.conf) with valkey equivalents
• Replace /etc/redis and /var/redis with valkey equivalent paths
• "redis_6379" -> "valkey_6379"

Part of #18

[stockholmux]

I think this was mostly just a search/replace PR but there are things that won't work here.

[zuiderkwast]

I added info about docker containers under the linux install page.

I updated the mac page to say "brew install valkey" and other commands like "brew services start valkey". I hope it works. :)

Let's improve this information later. I just want to delete wrong info for now.