Add governance policies

[afrittoli]

Add a number of policies and documents about CDEvents governance and processes. A lot of content is inspired by the Tekton community governance documents and adapted for CDEvents.

Key new things added:

• governing boards elections (eligibility, etc)
• contributor roles and ladder (eligibility, etc)

Some new mailing lists will have to be created.

The current bootstrap committee includes 5 individuals. My proposal is to keep a team of five. For continuity, I propose that

• We held elections for three of the seats, to ensure continuity in the project governance.
• Emil and Andrea have been acting as project governance since the beginning, so their seats that be maintained until after 1 year after the election
• Nattias, Erik and Steve seats are up for election

[afrittoli]

@cdevents/governance please let me know if this looks ok - once we have an agreed version, we can start the election process and create any missing GitHub team and email list

[afrittoli]

@m-linner-ericsson I see you have not approved the PR, do you have any remaining concerns?

[afrittoli]

Just a few more things. Then I'm pleased :)

Thanks for the through review, all fixed now.