[Feature] CNF installation (4), Create and use common manifest

[kosstennbl]

4th step of #2120.

Testsuite currently has methods for creation of manifest files from helm charts. As a part of CNF installation redesign, we need some changes for this process:

1. Add possibility to create combined manifest by adding manifests from different deployment methods (helm and manifest). (cnfs/common_manifest.yml)
2. Change test functionality to use common manifest in cases, where generated manifests are used.
3. Move all connected functionality to the tasks/utils/cnf_installation folder, rename manifest.cr to manifest_deployment.cr and create new manifest.cr that would be containing the code.

Prerequisites for this issue are: #2095, #2124.