Save last used SubGHZ config settings

[derskythe]

What's new

• Last used SubGHz settings in Read/ReadRAW are saving to separate file subghz/assets/last_used.txt
• Saving: Frequency, Modulation, Detect Raw, RSSI for Raw
• Settings file is created if missing

Verification

• Open SubGHz and go to Read or ReadRAW
• Go to Config and change settings
• Exit from SubGHz and open again SubGHz
• Changed settings at their places

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

[RogueMaster]

Thank you!