1339: Save Button Disabled During API Call, Disllowing Multiple Requests

[aayush6194]

Pull Requests Requirements

• The PR title includes a brief description of the work done, including the
  Issue number if applicable.
• The PR includes a video showing the changes for the work done.
• The PR title follows conventional commit label standards.
• The changes confirm to the OpenElis Global x3 Styleguide and design
  documentation.
• The changes include tests or are validated by existing tests.
• I have read and agree to the Contributing Guidelines of this project.

Summary

• Added isSubmitting to track the state of the API call.
• The Save Button disabled while isSubmitting is true.
• postToOpenElisServer() return a Promise, allowing to chain additional .then() handler