[cartservice] Update to .NET 7

[Kielek]

Changes

Update target and docker images to .NET7 for cartservice.

Merge Requirements

For new features contributions please make sure you have completed the following
essential items:

• CHANGELOG.md updated to document new feature additions
• [ ] Appropriate documentation updates in the docs N/A
• [ ] Appropriate Helm chart updates in the helm-charts N/A

Maintainers will not merge until the above have been completed. If you're unsure
which docs need to be changed ping the
@open-telemetry/demo-approvers.

[cartersocha]

The cart service is constantly restarting on my mac m2. Getting an error message like " Unhandled exception. System.TypeInitializationException: The type initializer for 'OpenTelemetry.SuppressInstrumentationScope' threw an exception.
cart-service | ---> System.NullReferenceException: Object reference not set to an instance of an object."

I can share the more detailed message if needed

[Kielek]

@cartersocha, I was able to reproduce. I am not sure how I missed that while testing (probably I have made mistake while building new docker image).

Bug reported under open-telemetry/opentelemetry-dotnet#4600

Locally, I have removed Trimming option. It will increase image size, but it is working correctly.

[cartersocha]

It's working now thanks!

[Kielek]

@cartersocha, trimming was working on .NET 6 by accident (it is producing warnings). There is a plan to make a support for trimming operation in OpenTelemetry .NET for 1.6 version (tentatively scheduled on November).

It should be good to merge for now.