Updating the readme and lib version to contain the changes from the latest stable release

[petyaslavova]

Pull Request check-list

Please make sure to review and check all of these items:

• Do tests and lints pass with this change?
• Do the CI tests pass with this change (enable it first in your forked repo and wait for the github action build to finish)?
• Is the new or changed code fully tested?
• Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?
• Is there an example added to the examples folder (if applicable)?
• Was the change added to CHANGES file?

NOTE: these things are not required to open a PR and can be done
afterwards / while the PR is open.

Description of change

Updating the readme and lib version to contain the changes from the latest stable release.
Also updating the test container image tag to match the latest stable Redis release.

[Copilot]

Pull Request Overview

Updating the library version and documentation to reflect the latest stable Redis release, while aligning test infrastructure with Redis 8.0.

• Bumped __version__ in redis/__init__.py to 6.0.0
• Updated default test container image tags in docker-compose.yml to point at Redis 8.0
• Revised README supported versions table and added a new section on the default search/query dialect

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
redis/init.py	Library version bump from 5.2.1 to 6.0.0
docker-compose.yml	Default image tags updated to 8.0-RC2-pre with explanatory comment
README.md	Supported Redis versions table refreshed and search dialect docs added

[vladvildanov]

LGTM