Add ability to customize center text in PieChart

[webdeck]

• [x] I've read, understood, and done my best to follow the *CONTRIBUTING guidelines.

What did you do?

ℹ Created a pie chart with center circle

What did you expect to happen?

ℹ Have the ability to customize the font/color of the center circle text

What happened instead?

ℹ Text is always 12 point font with labelOrBlack color

Charts Environment

Charts version/Branch/Commit Number: 4.1.0 Xcode version: 14.3 (14E222b) Swift version: swift-driver version: 1.75.2 Apple Swift version 5.8 (swiftlang-5.8.0.124.2 clang-1403.0.22.11.100) Platform(s) running Charts: iOS, ipadOS macOS version running Xcode: 13.3.1 (a) (22E772610a)

Demo Project

ℹ Demo