[MDS] UX Changes for 2.5 Release

[KrooshalUX]

GLOBAL APP TO DO:

• If an error is present on any page within the application due to a provided endpoint becoming unavailable or authentication failing, present user with a toast message appropriate to the error case

CATCH ALL (@KrooshalUX to update as scope is defined)

• Implement test authentication & test authentication error handling #27
• Improvements on empty states
• Individual messages for all in-line form input boxes
• Check for errors reaching endpoint when endpoint URL is input (onBlur and onChange)
• Improved toast messaging for API Create/Update errors (dependent on API changes)
• Improved input placeholder copy

[KrooshalUX]

Due to engineering priorities changing, these are no longer in scope. I will work with @kristenTian to ensure these line items are accounted for in subsequent releases. Closing for repo cleanliness.