Change Jenkins section to CI/CD

CI/CD will include Jenkins and other CI/CD systems.

In addition, added a couple of questions on various topics.

exercises/cicd/ci_for_open_source_project.md

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+## CI for Open Source Project
+
+1. Choose an open source project from Github and fork it
+2. Create a CI pipeline/workflow for the project you forked
+3. The CI pipeline/workflow will include anything that is relevant to the project you forked. For example:
+  * If it's a Python project, you will run PEP8
+  * If the project has unit tests directory, you will run these unit tests as part of the CI
+4. In a separate file, describe what is running as part of the CI and why you chose to include it. You can also describe any thoughts, dilemmas, challenge you had
+
+### Bonus
+
+Containerize the app of the project you forked using any container engine you would like (e.g. Docker, Podman).<br>
+Once you successfully ran the application in a container, submit the Dockerfile to the original project (but be prepared that the maintainer might not need/want that).
+
+### Suggestions for Projects
+
+The following is a list of projects without CI (at least at the moment):
+
+Note: I wrote a script to find these (except the first project on the list, of course) based on some parameters in case you wonder why these projects specifically are listed.
+
+* [This one](https://github.com/bregman-arie/devops-exercises) - We don't have CI! help! :)
+* [image retrieval platform](https://github.com/skx6/image_retrieval_platform)
+* [FollowSpot](https://github.com/jenbrissman/FollowSpot)
+* [Pyrin](https://github.com/mononobi/pyrin)
+* [food-detection-yolov5](https://github.com/lannguyen0910/food-detection-yolov5)
+* [Lifely](https://github.com/sagnik1511/Lifely)

exercises/cicd/remove_builds.md

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+### Jenkins - Remove Jobs
+
+#### Objective 
+
+Learn how to write a Jenkins script that interacts with builds by removing builds older than X days.
+
+#### Instructions
+
+1. Pick up (or create) a job which has builds older than X days
+2. Write a script to remove only the builds that are older than X days
+
+#### Hints
+
+X can be anything. For example, remove builds that are older than 3 days. Just make sure that you don't simply remove all the builds (since that's different from the objective).

exercises/cicd/remove_jobs.md

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+### Jenkins - Remove Jobs
+
+#### Objective 
+
+Learn how to write a Jenkins script to remove Jenkins jobs
+
+#### Instructions
+
+1. Create three jobs called: test-job, test2-job and prod-job
+2. Write a script to remove all the jobs that include the string "test"

exercises/cicd/solutions/remove_builds_solution.groovy

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+def removeOldBuilds(buildDirectory, days = 14) {
+
+  def wp = new File("${buildDirectory}")
+  def currentTime = new Date()
+  def backTime = currentTime - days
+
+  wp.list().each { fileName ->
+      folder = new File("${buildDirectory}/${fileName}")
+      if (folder.isDirectory()) {
+          def timeStamp = new Date(folder.lastModified())
+          if (timeStamp.before(backTime)) {
+            folder.delete()
+          }
+      }
+  }
+}

exercises/cicd/solutions/remove_jobs_solution.groovy

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+def jobs = Jenkins.instance.items.findAll { job -> job.name =~ /"test"/ }
+    
+jobs.each { job ->
+    println job.name
+    //job.delete()
+}