SFD-128: Add error summary for validation errors

[jantoun-scottlogic]

SFD-128 Jira ticket

Adds an error summary to display form validation errors. Includes links to the invalid input fields.

Notes:

• The 'calculate' button was previously disabled when there were validation errors. It has been enabled at all times but the error summary will be shown if there are validation errors. This is so that the error feedback is the same whether the form is submitted using the 'enter' key or the 'calculate' button.

Error summary:

Error summary dark mode:

[sdun-scottlogic]

Tested & Approved - SD.