Add updatedAt for GetBucketLifecycleConfig

[krisis]

Description

This will allow users to learn the most recent time when their bucket's ILM policy was updated.
The updatedAt timestamp is returned as part of GetBucketLifecycleConfig call as a response header like so,

X-Minio-Lifecycleconfig-Updatedat: 20230524T223706Z

Motivation and Context

Bucket ILM policies may be updated multiple times depending on an organization's evolving object lifecycle requirements. It can become difficult to reason with object lifecycle events like expiration, transition, etc without knowing when the ILM policy was last updated.

How to test this PR?

1. Configure ILM policy for a bucket
2. mc ilm ls --json ALIAS/bucket
   Requires Add updatedAt for ilm-rule-ls mc#4579 for testing

Sample output

{
 "status": "success",
 "target": "myminio/bucket",
 "config": {
  "Rules": [
   {
    "Expiration": {
     "Days": 200
    },
    "ID": "chn7t9lvvqdakbhfn73g",
    "Status": "Enabled"
   },
   {
    "ID": "chn934gd6vv3cmvlc5s0",
    "NoncurrentVersionExpiration": {
     "NoncurrentDays": 1
    },
    "Status": "Enabled"
   }
  ]
 },
 "updatedAt": "2023-05-24T22:37:06Z"
}

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:

• Fixes a regression (If yes, please add commit-id or PR # here)
• Unit tests added/updated
• Internal documentation updated
• Create a documentation update request here

[shtripat]

LGTM. Verified the changes with mc PR#4579