[Enhancement]: Add KeyDB support

Problem

Redis is no longer open-source, and the main two alternatives to it are:

• Valkey, which is a very young fork of Redis that offers pretty much the same feature-set as Redis before the switch to "source-available"
• KeyDB, which is a more mature fork of Redis that is more performant (multithreaded)

In my projects, I've switched to using KeyDB, which induced quite a bit of boilerplate for my tests that need a distributed cache, and I think that having a KeyDB module in Testcontainers.NET will be beneficial.

Solution

Introduce a KeyDB module.

Benefit

Support those that have opted to switch to KeyDB after the Redis fiasco.

Alternatives

The main alternative is supporting Valkey, which has also rapidly gained popularity, but, considering that KeyDB offers some unique features over Valkey, I see support of both as relevant.

Would you like to help contributing this enhancement?

Yes

No files, tests, or entry points are named. Start by locating the existing Redis-related module and its tests, then determine the module structure and container behavior that a KeyDB implementation must follow. Done means KeyDB support is exposed as a tested Testcontainers.NET module.