AppAuth version updated for Apple Privacy Manifest for AppAuth-iOS

[faizplus]

Fixes #954

Description

Updated the minimum version from 1.6 to 1.7.3 for AppAuth-iOS required by this package as it has the required privacy manifest included with it.

From the issue:

Apple's Privacy manifest requirement is required by May 1st.
https://developer.apple.com/news/?id=3d8a9yyh

AppAuth is mentioned in the SDKs that require a privacy manifest and signature:
https://developer.apple.com/support/third-party-SDK-requirements/

It looks like the AppAuth-iOS pod released the version that has the privacy manifest recently:
https://github.com/openid/AppAuth-iOS/releases/tag/1.7.3

Steps to verify

Run the Example app to verify the version installed by pod install

[changeset-bot]

🦋 Changeset detected

Latest commit: 87e75b1

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
react-native-app-auth	Minor

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[carbonrobot]

Looks good, please add a changeset for a minor release by running yarn changeset and following the prompts

[faizplus]

Looks good, please add a changeset for a minor release by running yarn changeset and following the prompts

Added changeset!