prioritize location of trigger.config.ts file to set the "base" path instead of package.json

[ericallam]

Some monorepo setups don't have a package.json inside the individual workspace (instead they just have 1 at the root of the monorepo), which messes up some path resolution logic during the dev command. We should use the trigger.config.ts file path instead of the package.json to determine the "base" path when running the dev command to fix this.