Refactor configuration and builder pattern

[XAMPPRocky]

This PR updates Quilkin's configuration to be more dynamic friendly, and to allow for the configuration to contain not just static or dynamic, but instead make endpoints, filters, and management_servers each optional fields which allows for us to reuse the same configuration on the xDS server side as we would on the Quilkin client side. The only change in behaviour here is that you can now set Quilkin's initial state before it connects to the management servers.

Breaking Changes

• Removed static and dynamic properties in Config, instead replacing them with endpoints, filters, and management_servers directly.
• Removed proxy::Builder, instead constructing Server from Config directly.

closes #520

[github-actions]

This PR exceeds the recommended size of 1000 lines. Please make sure you are NOT addressing multiple issues with one PR. Note this PR might be rejected due to its size.

[rezvaneh]

Nice work!

[bombsimon]

LGTM

[quilkin-bot]

Build Succeeded 🥳

Build Id: 03c78f04-8d47-4439-a51c-0155baa9ad0d

To build this version:

git fetch git@github.com:googleforgames/quilkin.git pull/525/head:pr_525 && git checkout pr_525
cargo build