fix: honor alias region configuration

[mrjavadseydi]

Contribution Licensing (no CLA, inbound=outbound, DCO required)

This pull request contributes to PGSTY SILO mcli (pgsty/mc). Code contributions are accepted under AGPL-3.0-or-later, the same license as the client. This project does not use a CLA or require a separate Apache-2.0 license grant. By submitting this pull request I represent that I have the right to contribute these changes under the GNU AGPL v3.0 or later. Every commit carries the required DCO Signed-off-by trailer.

Description

Honor the optional region field in version 10 alias configurations. Propagate the configured value to the S3 client while preserving MC_REGION and AWS_REGION precedence, and include the resolved region in the client cache identity.

Motivation and Context

S3-compatible services that do not implement GetBucketLocation can return an error even when the alias already specifies its region. Passing that region to minio-go avoids the unsupported lookup and signs requests with the configured region.

Addresses minio#5268.

How to test this PR?

• go test ./... -count=1
• go test -race ./cmd -run Test(S3ClientRegionPrecedence|S3ClientCacheKeepsRegionIdentity|GetConfigHashIncludesRegion) -count=1
• make install

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Optimization (provides speedup with no functional changes)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• All commits are signed off (git commit -s) per the DCO
• Fixes a regression (not a regression)
• Unit tests added/updated
• Internal documentation updated (not needed)
• Public documentation update opened in pgsty/silo.pgsty.com (not needed)