[exporter/otlphttpexporter] Use NewDefaultClientConfig instead of man… #2051

Job	Run time
govulncheck	29s
setup-environment	11s
test-coverage	6m 5s
unittest-matrix (ubuntu-latest, ~1.23)	2m 20s
checks	1m 59s
unittest-matrix (ubuntu-latest, ~1.22)	2m 14s
cross-build-collector (darwin, amd64)	39s
lint	3m 40s
cross-build-collector (darwin, arm64)	44s
cross-build-collector (linux, 386)	36s
cross-build-collector (linux, amd64)	44s
cross-build-collector (linux, arm64)	37s
cross-build-collector (linux, ppc64le)	44s
cross-build-collector (linux, arm, 7)	35s
cross-build-collector (linux, s390x)	38s
cross-build-collector (windows, 386)	46s
cross-build-collector (windows, amd64)	37s
unittest	1s
	23m 39s

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