create a new V2 endpoint for cluster SSH keys management

[zreigz]

What this PR does / why we need it: create a new V2 endpoint for cluster SSH keys management

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

create a new V2 endpoint for cluster SSH keys management:
PUT /api/v1/projects/{project_id}/dc/{dc}/clusters/{cluster_id}/sshkeys/{key_id}
GET /api/v1/projects/{project_id}/dc/{dc}/clusters/{cluster_id}/sshkeys
DELETE /api/v1/projects/{project_id}/dc/{dc}/clusters/{cluster_id}/sshkeys/{key_id}

[lsviben]

/lgtm
/approve

[kubermatic-bot]

LGTM label has been added.

Git tree hash: 5738a7523a96b5982221902aa02fbcec6261fcf3

[kubermatic-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: lsviben, zreigz

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• OWNERS [lsviben,zreigz]
• cmd/kubermatic-api/OWNERS [lsviben,zreigz]
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