Document the convention for the `serviceShort` value generation

[AlexanderSehr]

Guidelines should contain

• How characters are identified (e.g. camelCases of ProvideNamespace + camelCases of ResourceType + testFolderName)
• What the maximum length should be (as some resources like storage accounts may otherwise run into issues) - could use maxLength annotation - which is especially interesting for any deploy.test.bicep that deploys resources with name restrictions (e.g. storage accounts)