fix: Escape shell arguments for safety

[mrsafalpiya]

This pull request improves the security of shell command execution in backend/dockerMailserver.js by introducing proper escaping of user-supplied arguments. The most important changes include adding a utility function to escape shell arguments and updating all relevant command invocations to use this function, reducing the risk of shell injection vulnerabilities.

Security improvements for shell command execution:

• Added a new escapeShellArg function that safely escapes strings for use in shell commands by wrapping them in single quotes and escaping internal quotes.
• Updated addAccount, updateAccountPassword, and deleteAccount functions to use escapeShellArg for email and password arguments when invoking shell commands. [1] [2] [3]
• Updated addAlias and deleteAlias functions to use escapeShellArg for source and destination arguments in shell commands. [1] [2]