* Update IAM and S3 protobuf definitions for explicit IAM gRPC APIs
* Refactor s3api: Extract generic ExecuteAction method for IAM operations
* Implement explicit IAM gRPC APIs in S3 server
* iam: remove deprecated GetConfiguration and PutConfiguration RPCs
* iamapi: refactor handlers to use CredentialManager directly
* s3api: refactor embedded IAM to use CredentialManager directly
* server: remove deprecated configuration gRPC handlers
* credential/grpc: refactor configuration calls to return error
* shell: update s3.configure to list users instead of full config
* s3api: fix CreateServiceAccount gRPC handler to map required fields
* s3api: fix UpdateServiceAccount gRPC handler to map fields and safe status
* s3api: enforce UserName in embedded IAM ListAccessKeys
* test: fix test_config.json structure to match proto definition
* Revert "credential/grpc: refactor configuration calls to return error"
This reverts commit cde707dd8b.
* Revert "server: remove deprecated configuration gRPC handlers"
This reverts commit 7307e205a0.
* Revert "s3api: enforce UserName in embedded IAM ListAccessKeys"
This reverts commit adf727ba52.
* Revert "s3api: fix UpdateServiceAccount gRPC handler to map fields and safe status"
This reverts commit 6a4be3314d.
* Revert "s3api: fix CreateServiceAccount gRPC handler to map required fields"
This reverts commit 9bb4425f07.
* Revert "shell: update s3.configure to list users instead of full config"
This reverts commit f3304ead53.
* Revert "s3api: refactor embedded IAM to use CredentialManager directly"
This reverts commit 9012f27af8.
* Revert "iamapi: refactor handlers to use CredentialManager directly"
This reverts commit 3a14821223.
* Revert "iam: remove deprecated GetConfiguration and PutConfiguration RPCs"
This reverts commit e16e08aa00.
* s3api: address IAM code review comments (error handling, logging, gRPC response mapping)
* s3api: add robustness to startup by retrying KEK and IAM config loading from Filer
* s3api: address IAM gRPC code review comments (safety, validation, status logic)
* fix return
Chris Lu