doc: add clarification for length limit of init password

[simonmysun]

Related code:

dify/api/controllers/console/init_validate.py

Line 31 in 14f3d44

parser.add_argument("password", type=StrLen(30), required=True, location="json")

Summary

The init password has an implicit length limit. It the user sets a password longer than 30 characters in the .env file, they will not be able to submit to the web server in the init process. It's better to explicitly clarify this limit.

Screenshots

None. Please see diff.

Checklist

Important

Please review the checklist below before submitting your pull request.

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods