Documents required by Commonhaus

[manovotn]

As part of Commonhaus foundation, all Weld's non-archived projects need to adhere to foundation's requirements which include having the following documents in the repository:

• License
• Developer Code of Origin (DCO)
• Code of Conduct
• Contributing
• Governance

This PR aims add missing files or perhaps adjust existing ones. The governance doc might come slightly later as we need to sync that with WildFly Commonhaus org, which Weld is part of and as such needs to build on their governance ideas.

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EDIT: After some discussion, the documents for all Weld projects are to be housed in a separate repository - https://github.com/weld/.github
The only one needed in each repository is the license file.
I have adapted this PR accordingly.

There should also be a README file that points to these documents - I plan to add that in a separate PR.

[manovotn]

With this PR the main branch would now contain all of the needed documents.
That said, there is also an option to house them in a special .github project so that we needn't repeat it for every single project.
For instance Hibernate did this, see https://github.com/hibernate/.github/tree/main
However, at least license file should be present in all repos and it might be arguably "cleaner" to have them replicated in each repo. I am still not sure.

Last but not least, we should update the README file (here and in all other projects) with links to these respective documents so that anyone visiting the project can clearly get from README to some contribution guidelines, governance and more.

Other active Weld projects have similar PRs:

• Add missing documents to the repo weld.github.io#98
• Add missing documents to the repo parent#230
• Add missing documents to the repo api#236
• Add missing documents to the repo weld-core-benchmarks#2
• Add missing documents to the repo weld-testing#278
• Add missing documents to the repo command-context-example#3