feat: add toggle to SigV4AuthScheme to turn off body signing #3996

Job	Run time
apple (macos-14, Xcode_15.2, platform=iOS Simulator,OS=17.2,name=iPhone 15)	13m 1s
linux (jammy, 5.9)	9m 7s
apple (macos-14, Xcode_15.2, platform=tvOS Simulator,OS=17.2,name=Apple TV 4K (3rd generation) (a...	8m 17s
linux (jammy, 6.0)	10m 4s
apple (macos-14, Xcode_15.2, platform=visionOS Simulator,OS=1.0,name=Apple Vision Pro)	20m 25s
linux (amazonlinux2, 5.9)	9m 29s
apple (macos-14, Xcode_15.2, platform=macOS)	11m 7s
linux (amazonlinux2, 6.0)	9m 17s
apple (macos-15, Xcode_16.1, platform=iOS Simulator,OS=18.1,name=iPhone 16)	7m 12s
apple (macos-15, Xcode_16.1, platform=tvOS Simulator,OS=18.1,name=Apple TV 4K (3rd generation) (a...	6m 2s
apple (macos-15, Xcode_16.1, platform=visionOS Simulator,OS=2.1,name=Apple Vision Pro)	8m 40s
apple (macos-15, Xcode_16.1, platform=macOS)	7m 53s
	2h 0m 34s

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