Request form: .gov domain required data format

[AnnaGingle]

Story

As a user who relies on clear and accessible form instructions,
I want the form fields in the request form and domain management pages to have consistent and descriptive labels that communicate the expected data format,
so that I can input my information without confusion, ensuring the form fully complies with Section 508 accessibility standards.

Required data formats must be communicated to the user. An error message is not sufficient.

The What .gov domain do you want? and Alternative domains (optional) fields do not communicate the format requirements.
You can use the error messages as a starting point for the hint text.

• Enter the .gov domain you want without any periods.
• Enter the .gov domain you want. Don’t include “www” or “.gov.” For example, if you want www.city.gov, you would enter “city” (without the quotes).
  
  

Acceptance Criteria

• Update the design ensuring that the required input format is communicated (an error message alone is not sufficient to communicate the expected format).
• The design passes 5.B Label descriptive and 5.H Error prevention.
• A dev ticket is created to update the design and screen reader output.

Additional Context

• Grouping controls W3C
• Using the fieldset and legend elements GOV.UK
• ANDI Guide
• Trusted Tester docs

Issue Links

Will be completed as a part of #2699

Prioritization Comments

WCAG Conformance Level: 2.1 AA
WCAG Standard that applies:
3.3.2 - Labels or Instructions (Critical)
3.3.3 - Error Suggestion (Critical, partially supports)
Critical Failure if Not Met?: Not in this case, see below
Prioritization: High/Must Do
Reason: This issue addresses essential guidance on input formats that is necessary for users to enter accurate data without confusion. Currently, users who rely on form hints, especially those with screen readers or cognitive disabilities, may struggle with incorrect input if the expected format is only communicated after an error. Providing clear, descriptive labels and hints directly on the form fields significantly improves usability and aligns with Section 508 and WCAG standards. Given that this issue does not entirely prevent form submission but still impacts usability and compliance, it is rated as High / Must Do.

[Katherine-Osos]

@SamiyahKey Let's chat about this one before we prioritize it into a sprint.