redis: use local sockets for Alpine clients

[ashutosh-agrawal]

Why

The Alpine VS xcvrd and Python process-exit listener read local Redis databases through TCP even though the local Unix socket is available.

What changed

• Use Unix sockets for xcvrd APPL_DB, APPL_STATE_DB, and STATE_DB.
• Pass the existing Unix-socket option to the syncd Python process-exit listener.

Validation

• git diff --check
• This repository has no focused unit tests for these launch paths.
• No tests were run.

Scope

This changes only local Alpine VS Redis clients. It does not change raw redis-cli, chassis, remote DPU, BMC, or Redfish behavior.

[mssonicbld]

/azp run

[azure-pipelines]

No pipelines are associated with this pull request.

[ashutosh-agrawal]

Closing this vendor or platform draft to keep the Redis migration effort within the 25-open-PR limit. The branch is retained and queued for a later platform batch.