fix(Pinpoint): Fixing error decoding AWSPinpointEndpointProfile when attributes are set.

[sebaland]

Description of changes:

When the user sets user attributes to Pinpoint's AWSPinpointEndpointProfile, it's successfully encoded and stored in the Keychain. However, attempting to decode it back failed with an error.

Error unarchiving class `AWSPinpointEndpointProfile`: Error Domain=NSCocoaErrorDomain Code=4864 "value for key 'NS.objects' was of unexpected class 'NSMutableArray' (0x1ec41f220) [/Library/Developer/CoreSimulator/Volumes/iOS_21F79/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS 17.5.simruntime/Contents/Resources/RuntimeRoot/System/Library/Frameworks/CoreFoundation.framework].
Allowed classes are:
 {(
    "'NSDictionary' (0x1ec41edc0)
 )}

This was caused due to not setting the right classes on the AWSPinpointEndpointProfileUser decoding process.

Check points:

• Added new tests to cover change, if needed
• All unit tests pass
• All integration tests pass
• Updated CHANGELOG.md
• Documentation update for the change if required
• PR title conforms to conventional commit style

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.