do not add to list if the element exist already

[yangcao77]

Signed-off-by: Stephanie [email protected]

What does this PR do?:

This PR updates the add functions to only append to list if the element does not exist in current list.
Also updates unit tests to check for expected result.

Which issue(s) this PR fixes:

Fixes devfile/api#622

PR acceptance criteria:

Testing and documentation do not need to be complete in order for this PR to be approved. We just need to ensure tracking issues are opened.

• Open new test/doc issues under the devfile/api repo
• Check each criteria if:
• There is a separate tracking issue. Add the issue link under the criteria
  or
• test/doc updates are made as part of this PR
• If unchecked, explain why it's not needed

• Unit/Functional tests

• QE Integration test

• Documentation

• Client Impact

How to test changes / Special notes to the reviewer:

[kim-tsao]

Looks good. The only (optional) suggestion I have is to add additional command and component types for testing but since duplicate checks are only using the component name, it shouldn't make a difference.

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: kim-tsao, yangcao77

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