backup: update design of destination

[Xieql]

What type of PR is this?

/kind api-change

/kind design

What this PR does / why we need it:

the design of destination is changed,

so we need update api

ref #377

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

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[kurator-bot]

@Xieql: The label(s) kind/design cannot be applied, because the repository doesn't have them.

In response to this:

What type of PR is this?

/kind api-change

/kind design

What this PR does / why we need it:

the design of destination is changed,

so we need update api

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[hzxuzhonghu]

/lgtm

[kurator-bot]

[APPROVALNOTIFIER] This PR is APPROVED

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