Allow list or string as service type + test cases

[PatStLouis]

Addresses #81

@dbluhm Please let me know if anything else needs to be added here!

[dbluhm]

A few failing tests to take care of

[PatStLouis]

I removed the invalid services I added as they weren't handled properly, I left the valid service using an array.

I was expecting the following types to be rejected but they are not at the moment: True, "", "Some type".

Since this is out of scope for this PR I will leave it as so. Perhaps it would be interesting to consider updating to pydantic 2.0.3+ in the future if there is a need for more strict field validation and introduce field_validators. Field validators would allow to make more interesting validation such as ensuring there is no space in a string, validating the length of an array, etc...

Let me know if this is satisfactory

[dbluhm]

It's possible to do the same with Pydantic 1.x but it would be nice to move to 2.0 regardless. I'm satisfied with these checks for now. Thanks for the contribution!