Adding TOTP_ISSUER as settings value

[yopiti]

Description

Using the site name at this point doesn't always make sense. This gives you the possibility to set TOTP_ISSUER in the settings.py file and show this information in the TOTP app.

Motivation and Context

Depending on the setup, using the sitename could lead to just showing a short name instead of the application name / url.

How Has This Been Tested?

Code testing

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[claudep]

Might make sense, however this needs docs, tests and of course the test suite must pass.