[FSSDK-12026] add customHeaders option to polling config manager #1390

Job	Run time
lint	1m 24s
unit_tests (22)	2m 1s
unit_tests (20)	1m 59s
unit_tests (18)	2m 10s
unit_tests (24)	1m 49s
lint_markdown_files / lint	1m 9s
integration_tests / test	6s
fullstack_production_suite / test	5s
Coveralls coverage	4s
	10m 47s

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