Update steering committee membership requirements

[kflynn]

We'd like to change the requirement for Steering Committee members such that it's OK for committee members to have been responsible for a nontrivial Linkerd deployment in production within the last two years, rather than requiring responsibility currently. This change is meant to better reflect the reality of job moves in the tech industry: a member who, for example, changes jobs to an organization in the process of adopting Linkerd shouldn't be instantly disqualified because they don't yet have a production deployment to be responsible for!

[kflynn]

This change requires a majority of the maintainers to approve it. Please vote yes by putting a 👍 response on this comment, or no with a 👎. Thanks!!