Add high agency as a value of the company

Created by: ElizabethStirling

Back when I was onboarding, @nicksnyder linked me this Twitter thread on high agency, and I find it incredibly relevant to the kind of culture we have at Sourcegraph. We want to make sure everyone feels empowered to speak out for what they think is right, and we trust our coworkers to do the best for the company. I've come to realize that one of the things that I really enjoy about working here is the feeling of having that agency to act in a way that feels right, and not just accept whatever management says without question. I always feel that I have both the power and responsibility to push back if I disagree or don't understand, and I think that's a very valuable environment for everyone involved.

I see this agency being fostered in many ways, such as being handbook first, marking high agency as a requirement for the security role, and allowing developers innovation time. However, I don't have the insight into the non-engineering teams in the company, and so I want to make sure this resonates with them as well. I don't want our values to only reflect the experiences of the engineering team, and if this is not a value held throughout the org, then we shouldn't put it as a value. Though, I would argue that such an outcome should spur a discussion of why we don't value agency throughout the org.

As such, the purposes of this PR are

1. To get feedback on my interpretation of the culture and environment we're cultivating.
2. To get insight from other parts of the organization as to how this value resonates with them, and if it does, how it manifests in their team.
3. To get advice on how to better phrase and communicate this value, should we determine it resonates with all teams, not just my team.

I've assigned some people here who I specifically want a review from, but please add your review, especially if you're not from an engineering team, since I have much less insight into the inner workings and culture of other teams.