Add release 1.18 to metadata.yaml #5394
                
     Merged
            
            
          
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What type of PR is this?
/kind cleanup
What this PR does / why we need it:
Adds the impending 1.18 release series to metadata.yaml.
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 #
Special notes for your reviewer:
TODOs:
Release note: