Added ability to run without ext. services

[uglrl]

Make sure, you have done de following before merging this pull request:

• Your code is documented using doc comments.
• You added appropriate logging in your code.
• You added unit tests to all your implemented functions.
• You ran cargo format and cargo clippy to format your code and check for improvements.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.72%. Comparing base (fe9c32b) to head (2b74329).
Report is 11 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #151   +/-   ##
=======================================
  Coverage   92.72%   92.72%           
=======================================
  Files          41       41           
  Lines        1746     1746           
=======================================
  Hits         1619     1619           
  Misses        127      127           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[worldofjoni]

Nice that you worked on that @uglrl!
I think it would be cleaner to add a command line option to the existing executable for running in isolated demo mode as this is mainly a code duplication. Similar to how the help page or should_migrate is done.
That could be tricky, however, because of the generic type parameters.

[uglrl]

I thought about doing that, but decided against it, since it would make the normal code flow more difficult to read and understand.

[worldofjoni]

Alright. I think, however, that naming the fine just bin.rs inside the startup folder is very misleading---something like standalone_demo_bin.rs would be clearer.
Also, the usage of this standalone version should be mentioned in the backend readme.