Replace SimpleHttpClient (okhttp based) by JdkHttpClient (HttpURLConnection based) #2018

Job	Run time
build	55s
integration-test	1m 4s
test (8)	1m 8s
test (11)	1m 8s
test (17)	1m 33s
test (20)	1m 55s
markdown-link-check / markdown-link-check	1m 1s
markdown-lint-check / markdown-lint-check	7s
misspell-check / misspell-check	4s
shell-script-check / shell-script-check	4s
publish-snapshots (skipped)	3s
required-status-check	1s
	9m 3s

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