CLA Assistant roll out

[trexfeathers]

We will shortly be applying a new CLA - v5 - to the SciTools organization, affecting all repositories within. This will be managed by CLA Assistant.

• The CLA itself can be seen here.
• A demonstration of a CI check: https://github.com/SciTools-incubator/iris-esmf-regrid/pull/239#issuecomment-1781422917
• Branch protection rules will be applied to prevent merging without a ✔ from CLA Assistant.
• Using a CLA can discourage contributors; our decision to keep it is discussed briefly here: https://github.com/SciTools/cartopy/issues/1919#issuecomment-1679258852
• CLA Assistant has been activated as of 2023-12-22, but the more popular SciTools repositories have been initially exempted to give time to warn maintainers outside the UK Met Office, and to update documentation.
• It's not too late to make changes to the Summary section of the CLA, if anyone has any strong feelings, since there are only a few signatories so far (CLA changes invalidate previous signatures). 2024-02-22 now rolled out everywhere

[trexfeathers]

Roll-out tracker

Repo	CLA active?	Files to update	Needs dummy PR [^1]	Branch protection rule added?
cartopy	- [x]	- [x] .github/CONTRIBUTING.md - [x] .github/PULL_REQUEST_TEMPLATE.md SciTools/cartopy#2306	- [x] No	- [x]
iris	- [x]	- [x] docs/src/developers_guide/contributing_getting_involved.rst - [x] docs/src/developers_guide/contributing_ci_tests.rst - [x] docs/src/developers_guide/contributing_documentation_easy.rst SciTools/iris#5664	- [x] No	- [x]
cf-units	- [x]	- [x] .github/CONTRIBUTING.md SciTools/cf-units#398	- [x] No	- [x]
nc-time-axis	- [x]	- [x] CONTRIBUTING.md SciTools/nc-time-axis#192	- [x] No	- [x]
python-stratify	- [x]	- [x] N/A	- [x] No	- [x]
iris-grib	- [x]	- [x] CONTRIBUTING.md SciTools/iris-grib#371	- [x] No	- [x]
tephi	- [x]	- [x] N/A	- [x] No	- [x]
iris-sample-data	- [x]	- [x] N/A	- [x] Yes	- [x]
libmo_unpack	- [x]	- [x] CONTRIBUTING.md SciTools/libmo_unpack#24	- [x] No (file changes will need PR)	- [x]
twitter-scitools-iris	- [x]	- [x] N/A	- [x] Yes	- [x]
test-iris-imagehash	- [x]	- [x] CONTRIBUTING.md SciTools/test-iris-imagehash#82	- [x] No	- [x]
scitools.org.uk	- [x]	- [ ] README.md - [ ] /wiki/Contributors-License-Agreement-processing-details - [ ] /cla/* - [ ] signed_cla.html - [ ] build.py - [ ] documents/scitools_licensing.md - [ ] ~privacy.html~ already out-dated, needs help from UK Met Office legal - [ ] organisation	- [x] No (file changes will need PR)	- [ ]
workflows	- [x]	- [x] N/A	- [x] Yes	- [ ] SciTools/workflows#40
um_packing	- [x]	- [x] N/A	- [x] Yes	- [x]
mo_pack	- [x]	- [x] N/A	- [x] Yes	- [x]
marketing	- [x]	- [x] N/A	- [x] Yes	- [x]
voted_issues	- [x]	- [x] N/A	- [x] Yes	- [ ] Live and learn! SciTools/voted_issues#6
um_utils	- [x]	- [x] N/A	- [x] Yes	- [x]
scitools.github.com	- [x]	- [x] N/A	- [x] Yes	- [x]
test-tephi-imagehash	- [x]	- [x] N/A	- [x] Yes	- [x]
iris-test-data	- [x]	- [x] N/A	- [x] Yes	- [ ] SciTools/iris-test-data#91
iris-abf	- [x]	- [x] N/A	- [x] Yes	- [x]
.github	- [x]	- [x] N/A	- [x] Yes	- [x]

[^1]: Need an open PR for CLA Assistant to run against, which will get CLA Assistant listed as an option for use in a branch protection rule.