Remove dependency on the base64 gem #516

Job	Run time
test-opensearch (2.5)	3m 34s
test-opensearch (2.6)	2m 11s
test-opensearch (2.7)	2m 13s
test-opensearch-faraday-1 (2.6)	2m 1s
test-opensearch (3.0)	2m 4s
test-opensearch-faraday-1 (2.7)	1m 58s
test-opensearch (3.1)	1m 59s
test-opensearch-faraday-1 (3.0)	1m 48s
test-opensearch-faraday-1 (3.1)	1m 46s
test-opensearch (3.2)	2m 27s
test-opensearch-faraday-1 (3.2)	1m 47s
test-opensearch (3.3)	1m 52s
test-opensearch-faraday-1 (3.3)	1m 43s
test-opensearch (jruby-9.3)	2m 59s
test-opensearch-faraday-1 (jruby-9.3)	2m 7s
test-opensearch-security (2.5)	1m 54s
test-opensearch-security (2.6)	1m 57s
test-opensearch-security (2.7)	2m 1s
test-opensearch-security (3.0)	2m 8s
test-opensearch-security (3.1)	1m 45s
test-opensearch-security (3.2)	1m 42s
test-opensearch-security (3.3)	2m 4s
test-opensearch-security (jruby-9.3)	1m 39s
	47m 39s

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