docker (compose): test environment variable + network alias: `SAT_TEST_ENV_E2E` is set to `1` to indicate that e2e environment requirement are available (notably specific accounts and hosts created). The e2e tests needing it won't be launched if this variable is not set. A network alias is set for the backend at `sat.test` (to have a tld available, needed for some network libraries like OpenSSL).

version: "3.6"
services:

  sat:
    image: salutatoi/sat
    build: backend

  libervia:
    build: libervia
    depends_on:
      - sat