feat(authenticator): Allow customer to override error strings per exception type

[mattcreaser]

• PR conforms to Pull Request guidelines.

Issue #, if available: #181

Description of changes:
Customer can set the error content for a particular AuthException by setting a string like e.g. amplify_ui_authenticator_error_invalid_state to provide content for InvalidStateException

This applies to the AuthenticatorError content and to UnknownError snackbar messages. Other types of errors (field level errors, other snackbar messages) have specific strings that can already be replaced.

How did you test these changes?

• Can override strings on the Error content
• Can override strings in UnknownError messages.

Documentation update required?

• No
• Yes (Please include a PR link for the documentation update)

General Checklist

• Added Unit Tests
• Added Integration Tests
• Security oriented best practices and standards are followed (e.g. using input sanitization, principle of least privilege, etc)
• Ensure commit message has the appropriate scope (e.g fix(liveness): message, fix(authenticator): message, fix(all): message)

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

❌ Patch coverage is 52.04082% with 47 lines in your changes missing coverage. Please review.
✅ Project coverage is 32.64%. Comparing base (c60267d) to head (61a33eb).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #266      +/-   ##
==========================================
+ Coverage   32.59%   32.64%   +0.05%     
==========================================
  Files         100      100              
  Lines        4608     4622      +14     
  Branches      583      587       +4     
==========================================
+ Hits         1502     1509       +7     
- Misses       2950     2956       +6     
- Partials      156      157       +1     

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