Fix typos in plugin error log, comments and plugins developer guide

[thomasboni]

Hi, I've seen some typo while reading the codebase

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• All tests have passed. If this feature is not already covered by the tests, new tests have been added.
• The pull request is targeting the master branch.
• The code has been validated to compile successfully by running go vet ./....
• The code has been formatted properly using go fmt ./....

[github-actions]

All contributors have signed the CLA ✍️ ✅
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[thomasboni]

I have read the CLA Document and I hereby sign the CLA