With this change, we get rid of Elasticsearch across all of Tutor.
Instead, we run Meilisearch, which is much more lightweight in terms of
memory usage. Obviously, this is a (very) breaking change. Indexing
commands will be run during init, such that search should work as
before.

After the edx-search PR is merged and the dependency is upgraded in
edx-platform, we should remove the manual `RUN pip install ...` command.