Refine copy on "complete account" screen

[lukaslevert]

Once a customer has signed up for ads.brave.com, they are met with a "welcome" screen prompting their billing details and agreement of several disclaimers that are currently very verbose.

Separately, there's a need to add a disclaimer for supported languages that ad ops is requesting be put on the main landing page, however marketing strongly advises against this as it's not a best practice for acquisition and leads to homepage bloating that distracts and/or detracts from sign-ups that are crucial for email marketing.

To solve both these issues, I propose updating the copy on the "welcome" screen, and adding one for the language. Additionally, at the same time we do this, we (I) should add a page to ads-help.brave.com for "supported languages" which will be linked and updated over time with this disclaimer.

Here is the proposed copy:

Please review and agree to the following disclaimers and policies to continue:

[] I understand that first-party analytics are necessary for independent reporting. Learn more
[] I understand that I can only run ad campaigns in English, Spanish, and Portuguese.
[] I understand that payment is required before campaigns can be launched. Learn more

[] I have reviewed and agree to the Advertiser Privacy Policy and Terms of Service applicable to Brave Ads.

CC @tackley @IanKrieger @lukemulks @murphyd

[lukaslevert]

Here's a mock for the above solution:

[murphyd]

This looks good, thanks @lukaslevert.
cc: @lukemulks