doc: remove whitespaces in .env

Describe the bug

ERROR: In file ./.env: environment variable name 'CI_ENVIRONMENT ' may not contain whitespace.

Steps to reproduce

1. Follow https://code.podlibre.org/podlibre/castopod/-/blob/alpha/docs/setup-development.md
2. See the bug

Possible fixes

CI_ENVIRONMENT=development

database.default.hostname=mariadb
database.default.database=castopod
database.default.username=podlibre
database.default.password=castopod

Would it be useful to add these?:

app.baseURL="http://127.0.0.1:8080/"
app.adminGateway="cp-admin"
app.authGateway="cp-auth"