Allow to update the service account policy via CLI since RustFS Console allows

[kadishmal]

I can update the service account policy via RustFS Console, meaning the cluster allows this operation. Console calls:

URL: http://127.0.0.1:9001/rustfs/admin/v3/update-service-account?accessKey=ACCESS_KEY

However, rc doesn't allow to update an existing service account which is very inconvenient since we should be able to add new buckets to grant permissions for services. We cannot rely on the Console since our infrastructure is managed via code.

The current feature-set of the CLI is as follows:

$ rc admin service-account --help
Manage service accounts

Usage: rc admin service-account [OPTIONS] <COMMAND>

Commands:
  ls      List service accounts
  create  Create a new service account
  info    Get service account information
  rm      Remove a service account
  help    Print this message or the help of the given subcommand(s)

Options:
      --format <FORMAT>           Output format: auto-detect, human-readable, or JSON [possible values: auto, human, json]
      --json                      Output format: human-readable or JSON
      --no-color                  Disable colored output
      --no-progress               Disable progress bar
  -q, --quiet                     Suppress non-error output
      --debug                     Enable debug logging
  -H, --header <REQUEST_HEADERS>  Add an x-amz-* request header to signed S3 requests
  -h, --help                      Print help
  -V, --version                   Print version

[kadishmal]

Likewise, we should be able to update other properties as well like expiration date as well as description of the service account.