[cartservice] Update to .NET8

[Kielek]

Changes

Update cartservice to .NET8 which is new LTS release.

Replaces #1269
Fixes #1262

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.

[Kielek]

@austinlparker, there is a problem while restoring package. (probably the same as on main). Still do not know how to proceed.

[austinlparker]

hmm. https://devblogs.microsoft.com/dotnet/improving-multiplatform-container-support/

seems like building on qemu isn't really supported...? i wonder if the stuff in this could help

[Kielek]

@austinlparker, great findings!
I have adjusted Dockerfile and build process.
Differences - to build step we are using non-alpine - by default alpine is not working with grpc tools package.
The final base image is the same as before - alpine.

I do not have the arm64 env. to verify if the build will be working fine. Build logs looks promising. Austin, could you please check the results?

@richlander, is there any chance that you review changes in docker build process?

[mviitane]

Builds and runs fine. Verified with arm64 (apple).

[austinlparker]

Also tested locally and it seems to be working. Fingers crossed!