Add explanatory help text to text inputs on user profile settings page

What does this MR do?

Adds explanatory text under the following fields on the user profile settings page:

• twitter
• linkedin
• skype
• website
• location
• organization

Solution

Changes required:

• Help text should always be styled as secondary.
• Limit the width of the email, public email, commit email, preferred language, location, and website to 320px from our predefined input field widths.
• Limit the width of the Skype, Twitter, LinkedIn, and Organization to 240px from our predefined widths.
• add the 'username' placeholder to the Skype intput field
• add the '@username' placeholder to the Twitter input field
• add the 'website.com' placeholder to the Website input field. URLs without http:// or https:// work so we should make that clear.
• add the 'City, country' placeholder to the Location input field.
• add help text 'Your LinkedIn profile name from linkedin.com/in/profilename' below the LinkedIn input field.
• add help text 'Who you represent or work for.' below the Organization input field.

Screenshots:

before	after

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/53020

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer

Closes #53020 (closed)