[integration] Implement specific CircleCI workflows

[nor3th]

Use case

CircleCI should only build the connectors which were recently changed instead of building ALL connectors only because one line was changed in a single connector.

Current Workaround

All connectors are built and docker images deployed.

Proposed Solution

https://circleci.com/docs/2.0/configuration-cookbook/#execute-specific-workflows-or-steps-based-on-which-files-are-modified

Additional Information

If the feature request is approved, would you be willing to submit a PR?

I don't have any CircleCI experience, would be glad if somebody else could implement that