DEVDOCS-6151: [update] removed required label where necessary (#668)

<!-- Ticket number or summary of work -->
# [DEVDOCS-6151]


## What changed?
The Update Products (Batch) and Create a Product endpoints share the
product_Base schema. Therefore, I created a separate request schema for
each endpoint.

## Release notes draft

bug fix: Removed the incorrect required flag for the Update Products
(batch) to prevent confusion.

<!-- Provide an entry for the release notes using simple, conversational
language. Don't be too technical. Explain how the change will benefit
the merchant and link to the feature.

Examples:
* The newly-released [X feature] is now available to use. Now, you’ll be
able to [perform Y action].
* We're happy to announce [X feature], which can help you [perform Y
action].
* [X feature] helps you to create [Y response] using the [Z query
parameter]. Now, you can deliver [ex, localized shopping experiences for
your customers].
* Fixed a bug in the [X endpoint]. Now the [Y field] will appear when
you click [Z option]. -->
* 

## Anything else?
<!-- Add related PRs, salient notes, additional ticket numbers, etc. -->

ping {names}


[DEVDOCS-6151]:
https://bigcommercecloud.atlassian.net/browse/DEVDOCS-6151?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ