Add recaptcha for new addon submission upload

[KevinMind]

Fixes: mozilla/addons#15076

Description

Adds recaptcha for new addon submissions, behind a waffle switch.

Context

In order to combat spam uploads, we will enable the google recaptcha field on all new addon upload submissions.

This should NOT lead to a recaptcha being seen on each submission, but will include the field to decide if and when to display.

Testing

You can enable seeing the recaptcha by flipping developer-submit-addon-captcha on

1. navigate to the new submission page
2. choose "listed" or "unlisted" (You should test both)
3. click continue
4. Expect to see the captcha above the continue button.
5. upload a valid xpi
6. If you do not submit the recaptcha, expect the page to reload with an error that the field is required, otherwise you will continue.

Note: if the waffle flag is "disabled" expect 4 to not display the captcha and thus 6 will always let you continue (assuming other fields are valid)

Checklist

• Add #ISSUENUM at the top of your PR to an existing open issue in the mozilla/addons repository.
• Successfully verified the change locally.
• The change is covered by automated tests, or otherwise indicated why doing so is unnecessary/impossible.
• Add before and after screenshots (Only for changes that impact the UI).
• Add or update relevant docs reflecting the changes made.

[diox]

Missing a test around the captcha not being included (even if the waffle switch is active) for new versions submissions.

[diox]

(Please update the PR title before merging too)

[KevinMind]

@diox I'm not sure I understand this scenario?

Missing a test around the captcha not being included (even if the waffle switch is active)

If the switch is active, we include the field... so the test is testing where the captcha is not included.. how would that happen?

[diox]

"for new versions submissions." (not new add-ons). That's a different view, submit_version_upload(), where include_recaptcha is not passed.

[diox]

For your consideration, I don't necessarily think this is better, but we could do the waffle check in the view, just passing include_recaptcha=waffle.switch_is_active('developer-submit-addon-captcha') ?

[KevinMind]

I don't have a super strong opinion if the waffle check happens in the view or the form, but I think the waffle check should be distinct from the view logic, in fact it has to be.

We need to be able to control whether or not to show the feature, and separately whether the feature is avaialble (regardless if we want it or not)

I think given those requirements, having the waffle check in the form actually makes sense, it is totally internalized and centralized.

The expression of "intent" to include the recaptcha is still on the view level (where it belongs IMO)