Implement demographic survey form fields for Income Brackets

[knowtheory]

See #494 / this decision brief

Updated Design replaces the radio buttons to a text field for income entry.

Figma: https://www.figma.com/file/92ikhj1sHgm3c9jwKp0NHV/Mozilla-Rally-%E2%80%93-Add-on?node-id=2103%3A0

Expectation is that we'll need to store the specific value entered, but that it may need to be bucketed/categorized to one of the 41 ranges as found in this brief

Additional requirements:

• Append a "$" and comma(s) (if required) once focus is removed from the field
• Right align the field
• Require only numeric entry

Error States: potentially none?

• If we're able to restrict the field to just numbers, we do not need an error for other character entry (we should consider this for the zip code field as well)
• There is no specific minimum or maximum for this figure, but we could consider capping (though I don't know that it matters much if someone wishes to put 999999999, for example, as it just will be logged as "over 250k")

[knowtheory]

Let's hold off on implementing on this front until we can consult with @changecourse.

[changecourse]

Updated description above with designs and additional requirements.