feat: 12 new exercises

[UbioZur]

Adding the Following exercises:

• Pogos
• Copenhagen Side Plank
• Tibialis Raise
• Single-leg Balance

[x] The images are in .webp format with a white background.
[x] Corresponding folders have been created in app/src/main/assets/ with the correct id.
[x] The exercises.json is validated with the validate_exercises_json.py
[x] The instructions are clear and detailed.
[x] The ids are unique and there are no duplicates.

[UbioZur]

Few more exercises:

• Cossack Squat
• Bird Dog
• Snap Down
• Broad Jump
• Hollow Hold
• Single Leg RDL
• Suitcase Carry

[UbioZur]

And the one I couldn't get proper images for yesterday!

• Bent Knee Calf Raise