New Autofill API: let service set optional header and footer for dataset picker.

Test: atest CtsAutoFillServiceTestCases:FillResponseTest#testBuilder_setAuthentication_illegalState,testBuilder_setHeaderOrFooterInvalid,testBuilder_setHeaderOrFooterAfterAuthentication,testBuilder_build_headerOrFooterWithoutDatasets
Test: atest CtsAutoFillServiceTestCases:LoginActivityTest#testAutoFillOneDataset_withHeader,testAutoFillOneDataset_withFooter,testAutoFillOneDataset_withHeaderAndFooter
Test: atest CtsAutoFillServiceTestCases

Fixes: 69458670

Change-Id: I34be762968ffcad97dbf86898d3f1745bc8d4d64