website website: Adjust contributor progression guidelines to foster community growth

Checklist:

[ x] You have signed off your commits
[ x] Ensure you follow best practices from our guide. Contributing.
[x] You have included screenshots when changing the website style or adding a new page.

Description of your changes: A minor variation to the requirements of the Kubeflow membership agreement.

The suggestion is to start the reviewer vetting period from the first contribution rather than from membership.

As being owner and contributor of the Model registry component and part of the community what I observed is

The current process from new member to committer takes too long (7-12 months) in the best-case scenario.
There are artificial time constraints between stages that may be unnecessary.
IMO, it is not balanced towards fairness and community growth.
We should be placing the importance of observing contributions over time not artificially keeping someone out.
I do hope this encourages more active participation from new contributors, and recognize them quickly.
IMO, there is not much difference between the reviewer and member as both can do this task; it is more on the approver to trust the reviewer; time is not giving any trust, anyway, I did not make any changes there.
full disclaimer, I do have many associates who are trying to earn their stripes and mentioned to me that this is a concern.

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