feature/support checksum of downloaded repository iso file

[will4j]

What type of PR is this?

/kind feature

What this PR does / why we need it:

When export artifact using repository iso url, each time the command kk artifact export was run, the iso file downloaded before will be overwrite and download again, which indeed is very annoying.

if checksum of local iso file matched, downloading can be skip, and the checksum is available at kubekey release site.

take examples below:

spec:
  arches:
    - amd64
  operatingSystems:
    - arch: amd64
      type: linux
      id: ubuntu
      version: "18.04"
      osImage: Ubuntu 18.04.6 LTS
      repository:
        iso:
          url: https://github.com/kubesphere/kubekey/releases/download/v3.1.1/ubuntu-18.04-debs-amd64.iso
          checksum: b69de0e6c6b789200d2de4febe9e9b214a4539c0d49da5ea826fff634d3b966d

Which issue(s) this PR fixes:

Fixes #

Special notes for reviewers:

Does this PR introduced a user-facing change?

Support checksum check to avoid repeat downloading from repository iso file url.

Additional documentation, usage docs, etc.:

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
No data about Duplication

See analysis details on SonarCloud

[will4j]

/assign @pixiake

[pixiake]

@will4j Thanks for this contributions !
/lgtm
/approve

[ks-ci-bot]

LGTM label has been added.

Git tree hash: 1bcbe41478cc8fa650c5765fdb31aa2cb4979f81

[ks-ci-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: pixiake, will4j

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