Switch URL parameters to uppercase to pass-through parameters for external studies on youcanbookme

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# TL;DR
Change external study passthrough parameters from lowercase to all caps, so that child hashed ID can be picked up by youcanbook.me scheduling pages.

# Narrative
Youcanbook.me (along with Calendly) is one of the most common scheduling services used by external studies on Lookit.

As a researcher using an external scheduled study, it is very helpful to have an anonymized identifier to cross-reference demographic data that Lookit provides about families who click "Click here to participate", with the data that we collect from them on our external youcanbookme scheduling page, and ultimately with our study's datasheet. When families click "Click here to participate", Lookit dynamically tries to pass through the child's study hashed ID as a parameter, appending ?child=study_hashed_ID to the youcanbookme URL. However, youcanbookme can only accept shorthand codes in all caps, so it cannot pick up ?child=, only ?CHILD=.

As a result, I have no anonymized identifier I can use to directly link the demographic data Lookit provides with my study's datasheet. Instead, to ultimately link Lookit demographic data with our study's datasheet, I have to manually cross-reference the Lookit demographic data with data the parent entered on our external scheduling page using parent/child names, and then use a study identifier to cross-reference the data the parent entered on our external scheduling page with our datasheet.

# Acceptance Criteria
- [ ] Clicking "Click here to participate" on an external study generates a URL with the ?child= parameter (and other parameters) in all caps, e.g., ?CHILD=
- [ ] A youcanbook.me scheduling form with a hidden question set up to collect the shorthand code CHILD successfully collects the parameter
- [ ] A youcanbook.me confirmation email set up to include the shorthand code includes the child's study hashed id using the shortcode CHILD

# Implementation Notes
Youcanbook.me documentation on shortcode formatting for hidden questions:
* [Using Passthrough and Hidden questions on Booking Form](https://support.youcanbook.me/hc/en-us/articles/17871901664919-Using-Passthrough-and-Hidden-questions-on-Booking-Form#hidden)
* [Use Shorthand Codes to customize communications](https://support.youcanbook.me/hc/en-us/articles/17321222931607-Use-Shorthand-Codes-to-customize-communications#shorthandcodes)
* [Pre-fill your booking form and pass customer data through to YouCanBookMe](https://support.youcanbook.me/hc/en-us/articles/17321940609687-Pre-fill-your-booking-form-and-pass-customer-data-through-to-YouCanBookMe#questions)

Start by tracing the code path for the external study “Click here to participate” link and how passthrough URL parameters are generated. Verify the resulting URL and the documented YouCanBookMe CHILD shorthand behavior against each acceptance criterion, including confirmation-email use.

Written by the indexing model from the issue text.