Fix CallKit audio session late init

[NicolasBuquet]

Fix a bug in Element iOS : when the user answer a VoIP call from the "Answer" button in Element room timeline, very often, his correspondant can't hear him.

It's because the Audio Session is initialized too late. See https://developer.apple.com/forums/thread/64544 (7th post from Apple Engineer)

See this issue in Element Github: https://github.com/element-hq/element-ios/issues/7721

See this issue in Tchap: https://github.com/tchapgouv/tchap-ios/issues/1047

Pull Request Checklist

• [x] Pull request is based on the develop branch
• [x] Pull request contains a changelog file in ./changelog.d. See https://github.com/matrix-org/matrix-ios-sdk/blob/develop/CONTRIBUTING.md#changelog
• [x] Pull request includes a sign off

[NicolasBuquet]

@pixlwave @giomfo Can you have a look at this fix. It's quite urgent Tchap side. Thanx.