refactor: remove hardcoded passwords from configuration files

[deepsource-dev-autofix]

This PR improves security by externalizing all database passwords into environment variables and also includes minor documentation typo fixes.

Changes made:

• Password in Configuration File: The issue identified hardcoded passwords in the MSSQL, PostgreSQL, MySQL, and Firebird connection strings. Each plain-text password has been replaced with an environment variable placeholder (e.g., ${MSSQL_DB_PASSWORD}, ${POSTGRESQL_DB_PASSWORD}, ${MYSQL_DB_PASSWORD}, ${FIREBIRD_DB_PASSWORD}). This prevents secrets from being checked into source control and ensures that credentials are provided securely at deployment time. Please ensure these environment variables are defined in your runtime environment or CI/CD pipeline; feel free to adjust the variable names if they differ in your setup.
• Minor documentation fixes: Corrected inconsistent capitalization in comment text to enhance readability (changed “You should” to “you should” and “to choose a username” phrasing).

This Autofix was generated by AI. Please review the change before merging.

[deepsource-io]

Here's the code health analysis summary for commits 7184030..65dc3e8. View details on DeepSource ↗.

Analysis Summary

Analyzer	Status	Summary	Link
C#	✅ Success		View Check ↗

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