Add OuterExtensions encoding for TLS ECH client #6464

Job	Run time
build library (--enable-intelasm --enable-sp-asm --enable-mlkem --enable-lms --enable-xmss --enab...	38s
build library (--disable-asm)	32s
build library (--enable-intelasm --enable-sp-asm --enable-all-crypto --enable-mlkem --enable-lms ...	59s
build library (--disable-asm --enable-all-crypto --enable-mlkem --enable-lms --enable-xmss --enab...	50s
build library (--disable-asm --enable-mlkem --enable-lms --enable-xmss --enable-mldsa)	39s
build library (--enable-intelasm --enable-sp-asm)	35s
	4m 13s

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