WIP: Fix dev setup documentation

[colado]

This PR introduces some enhancements to the dev setup process:

• Adds some missing vars and values to some of the env.example files.
• Adds a couple minor changes to the local setup documentation.
• Makes a couple of enhancements to the link script to avoid some pitfalls I ran into while trying to run it.
• Aligns the docker compose file with the new v18+ layout.

[mitchdowney]

I know it's WIP, but changes are looking good. Thanks for your help!

[colado]

Doc:

• https://hub.docker.com/_/postgres#pgdata
• Change PGDATA in 18+ to /var/lib/postgresql/MAJOR/docker docker-library/postgres#1259

[colado]

Thanks @mitchdowney. I got everything to run locally. Just one more thing: in order to get the dummy data I had to sign up to Podcast Index and paste the keys on the env files of podverse-qa and podverse-workers (in order to run the make local_qa_init_data/npm run parser... commands respectively). The parser did run for quite a while so not sure if I was overdoing this part or that's how it's supposed to be? Once I understand this part better I could maybe add a couple lines in the doc to make it more clear.

Also I did have to change some of the values on the podverse-api's env file for it to connect to postgres successfully. Other than that everything worked :)