documentation: error handling, safe environment access, node and pnpm use, octokit instance passing

[supalarry]

1. Document creating custom error code and then having a custom throw function when an error is caught.
2. Document adding new environment variables first in Doppler and then in env.ts for save typed environment access
3. Document using .nvmrc via use nvm to use same node version locally as adaptly uses.
4. Document to use corepack enable at the root of repo to use pnpm that adaptly has.
5. Document that octokit should be passed as last argument, and payload as second last. Only exception is if there are optional arguments then they go last in functions.