[historyserver] Migrate S3 credentials to standard AWS environment variables

[ashutosh1807]

Context

Per #4653 (comment), the historyserver S3 implementation uses non-standard environment variables for credentials:

• AWS_S3ID instead of AWS_ACCESS_KEY_ID
• AWS_S3Secret instead of AWS_SECRET_ACCESS_KEY
• AWS_S3Token instead of AWS_SESSION_TOKEN

These should be migrated to the standard AWS environment variables so the historyserver follows AWS SDK conventions and works seamlessly with existing credential setups.

Scope

• Update historyserver/pkg/storage/s3/s3.go to read from standard AWS env vars
• Update any related documentation and Helm chart values

Ref: #4652, #4653

[Future-Outlier]

thanks for opening this PR, I agree that we should do this, here's the reference: https://docs.aws.amazon.com/sdkref/latest/guide/feature-static-credentials.html