Change OAI license to CSSL v1.0 (and others)

- all RAN code, CI code, configuration files, dockerfiles, in CSSL v1.0
- all deployment code (openshift, charts, ancillary files like shell
  scripts), in MIT
- documentation in CC-BY-4.0
- exceptions might apply and are listed in NOTICE
- there is a new LICENSES folder with all licenses
- CONTRIBUTIONS.md has been updated accordingly

For automated changes based on OAI PL v1.1:

    perl -i~ -0pe 's/\/\*.*Licensed to the OpenAirInterface.*openairinterface.org\n#?/\/*\n * SPDX-License-Identifier: LicenseRef-CSSL-1.0\n/s' **/*.{c,h,cpp}
    perl -i~ -0pe 's/\/\*.*Licensed to the OpenAirInterface.*openairinterface.org\n#?/\/*\n * SPDX-License-Identifier: LicenseRef-CSSL-1.0\n/s' **/*.ts
    perl -i~ -0pe 's/<!--.*Licensed to the OpenAirInterface.*openairinterface.org\n.*-->/<!-- SPDX-License-Identifier: LicenseRef-CSSL-1.0 -->/s' **/*.xml

The rest (cmake, files with missing license, cmake) manually.

CONTRIBUTING.md

@@ -1,3 +1,5 @@
+<!-- SPDX-License-Identifier: CC-BY-4.0 -->
+
 # Contributing to OpenAirInterface #
 
 We want to make contributing to this project as easy and transparent as possible.
@@ -26,5 +28,13 @@ Please refer to the steps described on our website: [How to contribute to OAI](h
 # License #
 
 By contributing to OpenAirInterface, you agree that your contributions will be
-licensed under the license described in the file [`LICENSE`](./LICENSE) in the
-root directory of this source tree.
+licensed under
+
+1. [CSSL v1.0 license](LICENSES/preferred/CSSL-v1.0.txt): for RAN and UE
+   related source code and test scripts
+2. [CC-BY-4.0](LICENSES/preferred/CC-BY-4.0.txt): All the documentation
+3. [MIT](LICENSES/preferred/MIT.txt): Orchestration (helm-charts, docker
+   compose)
+
+Certain files are using different licenses; you can read about them in
+[NOTICE](NOTICE).