GraphQL-879 Change description for createBraintreeClientToken mutation

[karyna-t]

[Braintree] Change description for createBraintreeClientToken mutation.

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds are green)

[magento-engcom-team]

Hi @lenaorobei, thank you for the review.
ENGCOM-5931 has been created to process this Pull Request
✳️ @lenaorobei, could you please add one of the following labels to the Pull Request?

Label	Description
Auto-Tests: Covered	All changes in Pull Request is covered by auto-tests
Auto-Tests: Not Covered	Changes in Pull Request requires coverage by auto-tests
Auto-Tests: Not Required	Changes in Pull Request does not require coverage by auto-tests

[magento-engcom-team]

@karyna-tsymbal-atwix thank you for contributing. Please accept Community Contributors team invitation here to gain extended permissions for this repository.

[ghost]

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