feat: add toggle to SigV4AuthScheme to turn off body signing #1282

Job	Run time
linux (jammy, 5.9)	11m 27s
apple (macos-14, Xcode_15.2, platform=iOS Simulator,OS=17.2,name=iPhone 15)	14m 51s
linux (jammy, 6.0)	12m 22s
apple (macos-14, Xcode_15.2, platform=tvOS Simulator,OS=17.2,name=Apple TV 4K (3rd generation) (a...	10m 8s
linux (amazonlinux2, 5.9)	11m 32s
linux (amazonlinux2, 6.0)	12m 29s
apple (macos-14, Xcode_15.2, platform=visionOS Simulator,OS=1.0,name=Apple Vision Pro)	18m 41s
apple (macos-14, Xcode_15.2, platform=macOS)	9m 16s
apple (macos-15, Xcode_16.1, platform=iOS Simulator,OS=18.1,name=iPhone 16)	9m 40s
apple (macos-15, Xcode_16.1, platform=tvOS Simulator,OS=18.1,name=Apple TV 4K (3rd generation) (a...	11m 40s
apple (macos-15, Xcode_16.1, platform=visionOS Simulator,OS=2.1,name=Apple Vision Pro)	11m 40s
apple (macos-15, Xcode_16.1, platform=macOS)	9m 9s
	2h 22m 55s

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