Add electronic signature capture to mobile flutter app (android/iOS/tablet)

NOTE: Application Source Code in Spanish!!!, but your new code can be in english. Requirements: - Add electronic signature capture in one of the forms. - If there is internet connectivity, call an endpoint and upload the signature image via POST. - If there isn't, store locally the image, and later on, once connectivity is reestablished, call an endpoint and upload the signature image via POST. Steps to get to the signature form: 1. Login 2. Tap second record 3. In the opened collapsible area, tap the yellow button "actividades asignadas" 4. In the new list, in the tab "Pendientes", tap the first item 5. On the new popup, type the number on top. 6. In the new screen, down below the signature capture image should be added. 7. Once the signature capture image is tapped, a white full screen (horizontal) area should be opened, so the user can use the full phone screen to sign. 8. Once the signature is taken, get back to the normal horizontal view and show the signature at the bottom of the screen (please refer to mocuk for a visual guide). 9. When the save button is clicked (bottom right green icon), after calling the existing endpoint, add the call to the endpoint that will upload the signature. 10. Once the image is uploaded, go back to the previous page. Steps 1-5 and 10 are already done, this project is to complete steps 6-9 Specs: Endpoint to store the signature: /api/v1/RegistroClinico/{id_actividad}/saveandclose Upload the image as a png with transparent background. Mandatory field: 1. Crear a variable in this page to control if the signature is mandatory or optional. 2. By default, should be false (hardcoded). 3. When the value is true (mandatory), it shouldn't allow to save without a signature.