Improve error handling and messages in the ModelPageLeave function

The current error messages are generic. Consider providing more specific error messages and potential solutions to the user. For example, suggest checking file permissions or running the installer as an administrator.

FileOpen $3 $0 w
${If} $3 == ""
    StrCpy $0 $0 $3
    ${If} $0 == "0"
        MessageBox MB_OK "Error: Cannot create .env file. Please check your permissions or run as administrator."
    ${Else}
        MessageBox MB_OK "Error: Cannot create .env file. Error code: $0. Try running as administrator."
    ${EndIf}
    Abort
${EndIf}

_Originally posted by @sourcery-ai[bot] in https://github.com/ClinicianFOCUS/clinicianfocus-installer/pull/4#discussion_r1797211806_

ClinicianFOCUS / clinicianfocus-installer

Improve error handling and messages in the ModelPageLeave function #11