Add a manual build for rlclientlib-manylinux-2_28-build (#59) #45

Job	Run time
build (ubuntu1804-build, vowpal_wabbit/ubuntu1804-build.Dockerfile, ./)	56s
build (ubuntu2004-build, vowpal_wabbit/ubuntu2004-build.Dockerfile, ./)	38s
build (centos7_6_1810-build, vowpal_wabbit/centos7_6_1810-build.Dockerfile, ./)	42s
build (manylinux2010-build, manylinux2010-build.Dockerfile, ./vowpal_wabbit/manylinux/)	3m 49s
build (manylinux2014_aarch64-build, manylinux2014_aarch64-build.Dockerfile, ./vowpal_wabbit/manyl...	1m 1s
build (manylinux2014_x86_64-build, manylinux2014_x86_64-build.Dockerfile, ./vowpal_wabbit/manylin...	52s
build (rl-manylinux2010-build, rl-manylinux2010-build.Dockerfile, ./reinforcement_learning/manyli...	34s
build (rl-manylinux-2_28-build, rl-manylinux-2_28-build.Dockerfile, ./reinforcement_learning/many...	46s
build (rl-ubuntu-1804, reinforcement_learning/ubuntu1804-build.Dockerfile, ./)	4m 3s
	13m 21s

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