Replace master/slave terminology with primary/replica

[ori0o0p]

[Description] Redis has officially replaced “master/slave” with “primary/replica”. Lettuce should align with Redis documentation and community standards to avoid harmful or outdated terminology and improve consistency for developers.

This issue proposes:

• Renaming user-facing terms from master/slave to primary/replica

[Scope]

• Public APIs: class names, method names, configuration properties, enums
• CLI examples and README
• Logs and exception messages

[Non-Goals]

• Functional changes to replication behavior
• Removing any existing aliases without a deprecation period

[Request] If maintainers agree with the direction, I can:

• Submit a PR with a terminology audit
• Propose API-level changes with deprecations
• Update docs and examples

[uglide]

Hi @ori0o0p

We're open to accept PR that deprecates but doesn't remove yet any of "old" names. Once it's done we can release it in next minor release.