feat: add toggle to SigV4AuthScheme to turn off body signing #1280

Job	Run time
apple (macos-14, Xcode_15.2, platform=iOS Simulator,OS=17.2,name=iPhone 15)	12m 8s
apple (macos-14, Xcode_15.2, platform=tvOS Simulator,OS=17.2,name=Apple TV 4K (3rd generation) (a...	13m 6s
apple (macos-14, Xcode_15.2, platform=visionOS Simulator,OS=1.0,name=Apple Vision Pro)	11m 8s
apple (macos-14, Xcode_15.2, platform=macOS)	8m 46s
apple (macos-15, Xcode_16.1, platform=iOS Simulator,OS=18.1,name=iPhone 16)	9m 45s
linux (jammy, 5.9)	11m 46s
apple (macos-15, Xcode_16.1, platform=tvOS Simulator,OS=18.1,name=Apple TV 4K (3rd generation) (a...	9m 23s
linux (jammy, 6.0)	13m 14s
apple (macos-15, Xcode_16.1, platform=visionOS Simulator,OS=2.1,name=Apple Vision Pro)	9m 21s
linux (amazonlinux2, 5.9)	11m 40s
apple (macos-15, Xcode_16.1, platform=macOS)	8m 29s
linux (amazonlinux2, 6.0)	13m 2s
	2h 11m 48s

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