[Port to dspace-9_x] Fix submission form's "serious" accessibility issues

[AndreaBarbasso]

References

• Fixes [Deque Analysis] Submission form's "serious" accessibility issues #1187 (this is a backporting of Fix submission form's "serious" accessibility issues #4777)
• Requires [Port dspace-9_x] Change style for date pickers DSpace#11800

Description

Added a11y features for "serious" problems occurring in the submission form.

Instructions for Reviewers

List of changes in this PR:

• Added necessary aria attributes in order to pass axe accessibility tests;
• Implemented live region messages for the upload progressbar and for submission error messages.

To test/review the PR, check that the functionality of the submission form has not been altered, and that a11y tests now do not contain serious issues.

Checklist

• My PR is created against the main branch of code (unless it is a backport or is fixing an issue specific to an older branch).
• My PR is small in size (e.g. less than 1,000 lines of code, not including comments & specs/tests), or I have provided reasons as to why that's not possible.
• My PR passes ESLint validation using npm run lint
• My PR doesn't introduce circular dependencies (verified via npm run check-circ-deps)
• My PR includes TypeDoc comments for all new (or modified) public methods and classes. It also includes TypeDoc for large or complex private methods.
• My PR passes all specs/tests and includes new/updated specs or tests based on the Code Testing Guide.
• My PR aligns with Accessibility guidelines if it makes changes to the user interface.
• My PR uses i18n (internationalization) keys instead of hardcoded English text, to allow for translations.
• My PR includes details on how to test it. I've provided clear instructions to reviewers on how to successfully test this fix or feature.
• If my PR includes new libraries/dependencies (in package.json), I've made sure their licenses align with the DSpace BSD License based on the Licensing of Contributions documentation.
• If my PR includes new features or configurations, I've provided basic technical documentation in the PR itself.
• If my PR fixes an issue ticket, I've linked them together.