test: upload integration server logs as artifacts (#8600)

# Which Problems Are Solved

Upload the integration test server logs as artifacts, even if the tests
fail.
Before this change logs where printed through the Makefile.
However if a test would fail, the logs wouldn't get printed.

# How the Problems Are Solved

- Add an extra build step that pushes `tmp/zitadel.log` and
`tmp/race.log.$pid` to artificats storage.
- Logs are no longer printed in the `core_integration_reports` Makefile
recipe.

# Additional Changes

Do not remove coverage data when generating the coverage report in
`core_integration_reports`. This is to prevent future "File not found"
erros when running the command repeatedly.

# Additional Context

Reported as internal feedback

.github/workflows/core-integration-test.yml

@@ -74,6 +74,15 @@ jobs:
           ZITADEL_MASTERKEY: MasterkeyNeedsToHave32Characters
           INTEGRATION_DB_FLAVOR: postgres
         run: make core_integration_test
+      -
+        name: upload server logs
+        if: always()
+        uses: actions/upload-artifact@v4
+        with:
+          name: integration-test-server-logs
+          path: |
+           tmp/zitadel.log
+           tmp/race.log.*
       - 
         name: publish coverage
         uses: codecov/codecov-action@v4.3.0