[CDF-26040] Warnings instead of errors when package fails to load (#2118)

# Description

A package may fail to load if a module requires an alpha flag that the
user hasn't enabled. Instead of producing an error, we show a warning.

## Changelog

- [x] Patch
- [ ] Skip

## cdf

### Improved

- Show a warning if a package cannot be loaded due to wrong path or
missing alpha flag

## templates

No changes.
