Add services after setup has already been completed

[Carbrex]

Closes #47
New services can now be added without ./lila-docker down.
Do ./lila-docker add-services to add new services, then select the new services you want to add.
Only the new ones among the selected services will be added.

Try on gitpod: https://gitpod.io/new/#https://github.com/Carbrex/lila-docker/tree/add-services-after-setup

[Carbrex]

These 2 tests

test tests::test_gitpod_lila_url ... FAILED
test tests::test_gitpod_lila_url_with_pr_context ... FAILED

sometimes fail randomly and sometimes pass when I run cargo test locally.

[Carbrex]

Nvm, they fail as they run concurrently, cargo test -- --test-threads=1 works fine.

[fitztrev]

Just tried it, looks great! Will test more later.

I wonder if it should still prompt for database setup. If search for instance is added, may need to re-run the seeder to populate elasticsearch.