Add Jenkinsfile for Continuous Integration Setup

[buriburi-nik]

This pull request introduces a Jenkinsfile to set up Continuous Integration for the mock-company-webapp repository. The Jenkinsfile includes two main stages: Build and Test.

• Build Stage: Executes the Gradle build task using ./gradlew assemble to compile the application.
• Test Stage: Runs unit tests using ./gradlew test to ensure code quality and correctness.

Additionally, the post-processing steps include:

• Collecting test results in JUnit format for easy reporting.
• Archiving build artifacts (JAR files) to allow for further deployment or inspection.

This CI setup will help maintain code quality by automatically running builds and tests on each commit.

To demonstrate the CI setup, I modified the SearchService class to return Collections.emptyList() to simulate a failing test case. This change has been validated by confirming that the CI pipeline fails as expected.

Please review the changes and let me know if there are any questions or further adjustments needed.