docker-driver compose labels support

[mindfl]

What this PR does / why we need it:

It's a trivial improvement for support docker compose labels in the loki docker-driver.

Which issue(s) this PR fixes:

Fixes #922

Special notes for your reviewer:

I don't have Go programming skills, but it's really simple fix, I think. Changes tested by manualy build, push, and install plugin.

Checklist

• Documentation added
• Tests updated

[CLAassistant]

All committers have signed the CLA.

[cyriltovena]

Nice what's a compose project ? a global name for a given compose file ?

[mindfl]

Nice what's a compose project ? a global name for a given compose file ?

It's a project name option from docker-compose command:

  -p, --project-name NAME     Specify an alternate project name
                              (default: directory name)

Loki label -> docker compose label:

• compose_project -> com.docker.compose.project
• compose_service -> com.docker.compose.service

[cyriltovena]

You need to CLA. I'll will take a look at it.

[cyriltovena]

LGTM