[Codacy] Define a constant instead of using this literal 'Invalid username or password.' 4 times. #1745

Codacy finding

• Repository: TransactionProcessing/SecurityService
• Codacy org: TransactionProcessing
• Codacy repo: SecurityService
• Codacy issue ID: 1f3341815b22e34f91cf008fa36bc09a
• Codacy issue: https://app.codacy.com/gh/TransactionProcessing/SecurityService/issues/1f3341815b22e34f91cf008fa36bc09a
• File: SecurityService.BusinessLogic/RequestHandlers/LoginRequestHandler.cs
• Line: 74
• Rule: SonarCSharp_S1192
• Severity: Warning

Message: Define a constant instead of using this literal 'Invalid username or password.' 4 times.