Build IntegrationTest package as part of CI pipeline

[simonjbeaumont]

Motivation

We have an package in a subdirectory in this repo that we can be used as an
integration test to gate changes to the various repos in Swift OpenAPI project,
including the runtime package.

This will likely be implemented by shallow cloning this repo in the pull
request pipelines of other projects and running a script, using swift package edit to override the dependency on the package being tested, and building the
integration test package.

Modifications

• Simplify the integration test package location and name.
• Add a CI script that runs the integration test with a package override.
• Run this script as part of the soundness pipeline.

Result

On each pull request, the integration test package will be built with the
changes proposed in the pull request.

Test Plan

The CI pipeline for this PR will run the integration test because it's been
added to the soundness script, which is run as part of an existing CI pipeline.

I have also validated this locally:

❯ docker-compose -f docker/docker-compose.yaml run --build soundness
...
** Running /code/scripts/check-for-broken-symlinks.sh...
** Checking for broken symlinks...
** ✅ Found 0 symlinks.
** Running /code/scripts/check-for-unacceptable-language.sh...
** Checking for unacceptable language...
** ✅ Found no unacceptable language.
** Running /code/scripts/check-license-headers.sh...
** ✅ Found no files with missing license header.
** Running /code/scripts/run-swift-format.sh...
** ✅ Ran swift-format with no errors.
** Running /code/scripts/check-for-docc-warnings.sh...
...
** ✅ Generated documentation with no warnings.
** Running /code/scripts/run-integration-test.sh...
** Checking required executables...
...
Build complete! (42.53s)
** ✅ Successfully built integration test package.
** ✅ All soundness check(s) passed.

Notes

This PR adds the integration test to the soundness script, but we probably want
to split this out into its own pipeline.

[czechboy0]

Looks great, thank you @simonjbeaumont. Added one suggestion, otherwise you can land this. Up to you whether we land this as part of soundness now, or wait for the dedicated CI pipeline, either order is fine with me.

[simonjbeaumont]

Thanks @czechboy0.

Up to you whether we land this as part of soundness now, or wait for the dedicated CI pipeline, either order is fine with me.

If we land this in stages we can get the benefit now. After this PR it will be working. We can then add another pipeline and then remove it from soundness.

[czechboy0]