[Backport release-24.05] nixos/etc: support direct symlinks with etc overlay #321794

Evaluator Performance Report

stat	before	after	Δ	Δ%
cpuTime	655.92	655.98	↗ 0.06	0.01%
envs-bytes	20,987,163,472	20,987,163,472	0
envs-elements	1,105,134,226	1,105,134,226	0
envs-number	759,130,604	759,130,604	0
gc-heapSize	59,311,628,288	59,311,624,192	↘ 4,096	-0.00%
gc-totalBytes	130,031,121,216	130,031,130,352	↗ 9,136	0.00%
list-bytes	3,658,981,544	3,658,981,544	0
list-concats	83,739,034	83,739,034	0
list-elements	457,372,693	457,372,693	0
nrAvoided	879,507,675	879,507,675	0
nrFunctionCalls	697,869,268	697,869,268	0
nrLookups	364,815,429	364,815,429	0
nrOpUpdateValuesCopied	1,894,463,540	1,894,463,540	0
nrOpUpdates	86,140,630	86,140,630	0
nrPrimOpCalls	363,944,386	363,944,386	0
nrThunks	1,082,084,314	1,082,084,314	0
sets-bytes	42,976,577,184	42,976,577,184	0
sets-elements	2,524,179,767	2,524,179,767	0
sets-number	161,856,307	161,856,307	0
sizes-Attr	16	16	0
sizes-Bindings	16	16	0
sizes-Env	16	16	0
sizes-Value	24	24	0
symbols-bytes	2,466,811	2,466,811	0
symbols-number	172,215	172,215	0
values-bytes	33,363,348,048	33,363,348,048	0
values-number	1,390,139,502	1,390,139,502	0