Persistent Configuration Not Saving After Having Previously Been Removed

[caronc]

🪲 Describe the bug
Based on what was reported in this ticket, specifically this comment, it has been reported that a working configuration can just abruptly stop working. In the scenario given (where key is the same in all cases):

1. configuration was successfully saved using /add/{key}
2. configuration was successfully retrieved using /get/{key}
3. configuration was successfully removed using /del/{key}
4. configuration was (reported to be) successfully saved using /add/{key}
5. configuration was NOT successfully retrieved using /get/{key}

💻 Reported System Details:

• OS: Windows
• Python Version: n/a

🔮 Additional context
n/a

[caronc]

I was unable to reproduce this issue, but the added tests created from the Pull Request were still worth merging into the source code. It also made it so the format entry is no longer a requirement when setting a new config since Apprise is smart enough to detect what the configuration format is now.