WIP: Migrate to ESM

[lazerwalker]

This:

• Upgrades our TS version for the latest goodness
• Sets type: module to tell Node that all .js files are ESM
• Tells TypeScript to emit ESM instead of commonJS

Not currently mergable because Azure Functions doesn't seem to support type: module. A few options:

1. Write a manual build script to rename all .js files to .mjs, and remove type: module
2. Use node's default HTTP module instead of node-fetch
3. Give up on our Discord mod bot integration
4. Hope I get a better answer internally

[lazerwalker]

No action taken for 2022, Travis downgraded node-fetch.

For future-us, TS 4.7 includes support for mts files that compile down to mjs. Moving all of our files to mts/mjs should allow this to Just Work on Azure Functions.