Migrate all 'action' code to the new internal actions package to reduce
the number of internal packages.
Migrate the Bundle type to a separate package to avoid circular
dependencies.
Refactor code around bundle definition and download for relevant
services.
Changes:
- Most of the go code is now located in internal packages.
- Code refactored and simplified in some cases.
- Removed the 'download' mage target and integrated the download code
into the internal 'prepare' package.
- Moved all mage target code to magefile.go.
- Added missing descriptions to the mage targets.
- Updated go.mod.
Fixed:
- Created a custom function to validate the checksum of the
downloaded Woodpecker tar file.
- Specified the environment when running 'clean'.
