[Server] Implement Gradle subprojects and scaffolding for the Python server. (#1366)

.github/workflows/ci.yml

ci.mk

codegen-server-test/build.gradle.kts

codegen-server-test/python/build.gradle.kts

codegen-server-test/python/model

codegen-server/build.gradle.kts

codegen-server/python/build.gradle.kts

...t/codegen/server/python/smithy/RustCodegenServerPlugin.kt

...F/services/software.amazon.smithy.build.SmithyBuildPlugin

...thy/rust/codegen/server/smithy/RustCodegenServerPlugin.kt

settings.gradle.kts

...ild/scripts/check-server-codegen-integration-tests-python

...s/ci-build/scripts/check-server-codegen-unit-tests-python

tools/codegen-diff-revisions.py