Add LighthouseRunConfig model

[ecumike]

Instead of a hard-coded Lighthouse run config setting, rttms / requestLatencyMs / throughputKbps / ... etc used on all tests, add the ability to for an admin to sign in and create a Lighthouse run config profile. This would allow different settings to be used for running a test, instead of having one set hard-coded in the node config.js file.

For example, a model where "mobile", "desktop", "slow 3g" profiles can be created with appropriate settings.

Lighthouse run config settings we need fields for:

• rttMs
• requestLatencyMs
• downloadThroughputKbps
• uploadThroughputKbps
• throughputKbps
• cpuSlowdownMultiplier