Separte the image build

[choplin]

Description

Currently, the image build of scalardb-analytics-postgresql does all of the process, including downloading dependent FDW libraries, building them, and building scalardb-analytics-postgrsql, within a single build stage.

However, we would normally need to build scalardb-analytics-postgrsql, but we don't need it for the dependencies since they are less frequently changed. It would be a waste of computing time to build all of the dependencies every time.

Planned action

• Separate the image build process into two: building the dependencies and building the scalardb-analytics-postgresql
• Publish the former image to our docker registry, and use it as a base image for the latter.