ci: add workflow disptach to test cases

[danishedb]

Currenlty the workflows tests-cluster-chainsaw.yaml, tests-operator.yml and tests-plugin-barman-cloud.yaml Only runs on a pull request.
There shall be a way to use it on demand where we can run while adding editing test cases on CI.

Proposal: add workflow dispatch on each actions mentioned above.

[danishedb]

@itay-grudev Need your Approval on this.