[FEATURE] Add support to official clickhouse-connector

[PierreF]

Following #131, I'm going to work on a PR to add support for https://github.com/ClickHouse/clickhouse-connect

I'm going to work on a PR which add clickhouse-connect, so both clickhouse-connect and clickhouse-driver. The rational for this choice is:

• I fear the change might a bit consequent and have new clickhouse-connect an opt-in seems safer
• clickhouse-connect does not support native protocol, only HTTP protocol, which imply a breaking change

I could think of two way to support this:

• Either have two "ENGINE", like clickhouse_backend.backend and clickhouse_backend.backend_http
• Or add a flag to say which driver to use.

I think the flag version is better, e.g. something like:

DATABASES = {
    "clickhouse": {
        "ENGINE": "clickhouse_backend.backend",
        [...]
        "PORT": "8123",
        "OPTIONS": {
            "USE_HTTP_PROTOCOL": True,  # Or should it be "USE_CLICKHOUSE_CONNECT" ?
        },
    },
}

If I encounter other choice while working on the PR, I'll comment on this issue.