KAFKA-20881: Select the correct Connect module JAR in system tests

[majialoong]

Connect system tests currently add the first JAR returned by os.walk
to the worker classpath, which may select a javadoc JAR instead of the
executable module JAR.

This change uses DEV_VERSION to construct and select the exact
expected JAR for each Connect module, removing the dependency on
filesystem traversal order.

Reviewers: PoAn Yang payang@apache.org, Ken Huang
s7133700@gmail.com, Chia-Ping Tsai chia7712@gmail.com

[majialoong]

Tested locally with:

./gradlew clean
./gradlew -p connect javadocJar
TC_PATHS=tests/kafkatest/tests/connect bash tests/docker/run_tests.sh

Result:

================================================================================
SESSION REPORT (ALL TESTS)
ducktape version: 0.14.0
session_id:       2026-08-04--001
run time:         183 minutes 44.404 seconds
tests run:        145
passed:           145
flaky:            0
failed:           0
ignored:          0
================================================================================

[m1a2st]

Thanks, LGTM

[chia7712]

As long as we only add dev version files, this approach is safe and simpler