Fix/grant deletion hang after user is removed error 1141

[alereca]

Description of your changes

Fixes #47

I have:

• [x] Read and followed Crossplane's contribution process.
• [x] Run make reviewable to ensure this PR is ready for review.

How has this code been tested

Add unit tests for grant controller observe method:

• SuccessDiffGrantUsage

Update unit tests for grant controller observe method:

• SuccessDiffGrantNoDatabaseNoTable
  • Since this issue does not happen when a database is provided, as the default mysql behavior of granting USAGE to *.* does not affect grant observe comparison between actual and requested in resource spec privileges

[alereca]

@Duologic would you recommend keeping the old file name examples/mysql/grant.yaml or updating to examples/mysql/grant-database.yaml which I consider to be more descriptive?

[Duologic]

Rename sounds good. 👍