Add changelog for 2.20.1

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changelog 2.20.1

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Changelog

Features

• Optimized memory usage in Directions API model classes by interning frequently occurring strings in JSON. [#7840](https://github.com/mapbox/mapbox-navigation-android/pull/7840)

Bug fixes and improvements

• Fixed UI jank caused by on-device TextToSpeech player. [#7833](https://github.com/mapbox/mapbox-navigation-android/pull/7833)

Known issues ⚠️

Other changes

Android Auto Changelog

Features

Bug fixes and improvements

• The app is now considered as the one in active navigation only when an active route is set to MapboxNavigation. Previously it was always considered active. [#7366](https://github.com/mapbox/mapbox-navigation-android/pull/7366)
• When Android Auto host tells the app to stop active navigation because another app starts navigating, now SDK will enter FreeDrive mode instead of stopping trip session completely. [#7366](https://github.com/mapbox/mapbox-navigation-android/pull/7366)