add grafana user

[lpatte]

Description

Manage grafana in the generic database user resources.
Grafana do not allow to create user but now you can map the already created "avnadmin" user with a resource to reset it password

Fixes #407

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

• make testacc TESTARGS="-run TestAccCloudProjectDatabaseUser_basic"
• make testacc TESTARGS="-run TestAccCloudProjectDatabaseUserDataSource_basic"
• make testacc TESTARGS="-run TestAccCloudProjectDatabaseUsersDataSource_basic"

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings or issues
• I have added acceptance tests that prove my fix is effective or that my feature works
• New and existing acceptance tests pass locally with my changes
• I ran succesfully go mod vendor if I added or modify go.mod file