fbt fixes & improvements

[hedger]

What's new

• building updater targets no longer need explicit --with-updater flag - it is set internally
• flash_usb now only flashes .dfu file. For complete package, use flash_usb_full
• Added updater_minpackage target for building update package ony with .dfu file. Now used for flash_usb
• Fixed lookup of application.fam files; changed manifest processing errors from critical events to warnings

Verification

• Invoke flash_usb, flash_usb_full targets
• Create an empty folder in applications and a second one with invalid application.fam file
• Try building firmware

Checklist (For Reviewer)

• [ ] PR has description of feature/bug or link to Confluence/Jira task
• [ ] Description contains actions to verify feature/bugfix
• [ ] I've built this code, uploaded it to the device and verified feature/bugfix

[github-actions[bot]]

Compiled firmware for commit 730e1937:

• 📦 Update package
• 📥 DFU file
• ☁️ Web updater