add mutex

[wnxn]

What type of PR is this?

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/kind api-change
/kind bug
/kind cleanup
/kind design
/kind documentation
/kind failing-test
/kind feature
/kind flake

What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #40

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

Add mutex to handle more than one call "in-flight" per resource at the same time

Additional documentation e.g., usage docs, etc.:

[ks-ci-bot]

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This pull-request has been approved by: wnxn

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