Support GitHub Enterprise server in plugin/load_db service #3018

Job	Run time
env-protect-setup	7s
authorize	4s
get-dev-image / get-image	7s
clang-tidy	54s
generate-matrix	2m 45s
code-coverage	0s
build-and-test (Go race detector, nokvm, --config=go_race --compilation_mode=opt, bazel_buildable...	2m 48s
build-and-test (Clang opt + UI, nokvm, --config=clang --compilation_mode=opt, bazel_buildables_cl...	9m 24s
build-and-test-status	2s
	16m 11s

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