Add support for remote-execution / caching of signapk actions

Test: "RBE_SIGNAPK=true RBE_SIGNAPK_EXEC_STRATEGY=remote ... use_rbe m" on crosshatch-userdebug and
signapk targets worked
Bug: b/156765091

Change-Id: I4b8c21320c2f38914ef39d3d8f036d885fab4e72
Merged-In: I4b8c21320c2f38914ef39d3d8f036d885fab4e72