Improve API Error Message for Collection Alias Validation

Description:
When attempting to create a collection with an alias consisting only of numbers (e.g., 888), the API returns a technical error message:

"Identifier is not valid. Valid characters are a-Z, 0-9, '_', and '-'."

This message is misleading to the end user because it suggests that numbers are allowed, but in reality, an alias must contain at least one letter.

Proposed Fix:

Update backend validation logic to return a clearer message, e.g.:

"Invalid alias. Use letters (A–Z, a–z), numbers (0–9), underscores (_), or hyphens (-), and include at least one letter."

Steps to Reproduce:

1. Go to API endpoint for creating a Dataverse collection.
2. Set alias to a numeric-only string (e.g., 888).
3. Observe returned error message.

Expected Result:
A user-friendly and accurate error message explaining that numeric-only aliases are not allowed.

https://github.com/user-attachments/assets/45c804b6-7d30-4912-8eb5-648d83816262

Start with the backend alias validation used by the collection-creation API and reproduce the behavior with the numeric-only alias 888. Trace where the current identifier error is formed, then verify that the response explains the requirement for at least one letter while still documenting the permitted characters.