Implement batch expiration for permanent deletes of expired objects

[harshavardhana]

Description

Implement batch expiration for permanent deletes of expired objects

Motivation and Context

expire:
  apiVersion: v1
  bucket: BUCKET
  prefix: PREFIX
  # optional flags-based filtering criteria
  # for all objects
  flags:
    filter:
      newerThan: "7d" # match objects newer than this value (e.g. 7d10h31s)
      olderThan: "7d" # match objects older than this value (e.g. 7d10h31s)
      createdAfter: "date" # match objects created after "date"
      createdBefore: "date" # match objects created before "date"
      tags:
        - key: "name"
          value: "pick*" # match objects with tag 'name', with all values starting with 'pick'
      metadata:
        - key: "content-type"
          value: "image/*" # match objects with 'content-type', with all values starting with 'image/'
    notify:
      endpoint: "https://notify.endpoint" # notification endpoint to receive job status events
      token: "Bearer xxxxx" # optional authentication token for the notification endpoint
    retry:
      attempts: 10 # number of retries for the job before giving up
      delay: "500ms" # least amount of delay between each retry

How to test this PR?

You would need two PRs

• add 'expire' batch job madmin-go#213
• add 'batch expire' support mc#4650

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

[krisis]

Suggested change

	skip := func(info FileInfo) (ok bool) {
	filter := func(info FileInfo) (ok bool) {

opts.WalkFitler takes a function which returns true if the entry should be returned as part of the Walk calls results. skip gives the opposite impression/idea. This is a minor change but will help future readers understand the intent better.