add missing ffmpeg package for dev

[rafel-roboflow]

What does this PR do?

add ffmpeg package for dev docker

Type of Change

• Other: missing package

Testing

• I have tested this change locally
• I have added/updated tests for this change

Test details:

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code where necessary, particularly in hard-to-understand areas
• My changes generate no new warnings or errors
• I have updated the documentation accordingly (if applicable)