fix: dockerfile, pghrep build

Description

• Improved Dockerfile (~30 MB)
• pghrep should be build manually if checkup is running from sources
• README updates
• minor fixes in CI

Related issue

Examples

Checklist

• the MR description has been reviewed
• this MR contains text changes and they have been reviewed OR there are no texts changes
• this MR contains GUI/CLI changes and they have been reviewed OR there are no GUI/CLI changes
• this MR contains API changes and they have been reviewed OR there are no API changes