Standardize ROUTING_OBSTRUCTIONS (or GRT_OBS for OL1) for IPs

[amm-efabless]

Some IPs might require a lot of stuff intended for config.json that will make them integrate properly. An example is ROUTING_OBSTRUCTIONS (which should instead be GRT_OBS for OpenLane 1) which might not otherwise be obvious to the user:

caravel_user_sram/openlane/SRAM_1024x32/config.json

Lines 60 to 66 in 781c046

	"ROUTING_OBSTRUCTIONS": [
	"met1 0 40 314 435",
	"met2 0 40 314 435",
	"met3 0 40 314 435",
	"met4 0 40 314 435",
	"met5 0 40 314 435"
	],

For OL1 & OL2, can these be managed another way, instead of via explicit config.json entries? e.g. Keepouts in GDS or LEF, or some sort of dynamic config?