feat: display publishConfig during config list

[lukekarrys]

Closes: npm/statusboard#417

If the file at $NPM_CONFIG_PREFIX/package.json contains a
publishConfig, the key/value pairs will be printed along with the rest
of the output from npm config ls.

[npm-robot]

no statistically significant performance changes detected

timing results

app-large	clean	lock-only	cache-only	cache-only peer-deps	modules-only	no-lock	no-cache	no-modules	no-clean	no-clean audit
npm@8	52.508 ±0.30	37.068 ±0.34	28.826 ±7.28	25.692 ±0.97	3.698 ±0.04	3.744 ±0.02	2.981 ±0.09	15.889 ±0.14	3.027 ±0.04	3.859 ±0.01
#4146	52.706 ±0.49	37.432 ±0.78	28.964 ±7.62	27.012 ±0.12	3.667 ±0.02	3.702 ±0.01	3.006 ±0.03	15.959 ±0.02	3.089 ±0.12	4.194 ±0.10

app-medium	clean	lock-only	cache-only	cache-only peer-deps	modules-only	no-lock	no-cache	no-modules	no-clean	no-clean audit
npm@8	39.634 ±1.62	28.291 ±0.13	16.707 ±0.23	18.119 ±0.62	3.337 ±0.06	3.431 ±0.08	3.141 ±0.04	11.619 ±0.18	2.877 ±0.04	3.601 ±0.07
#4146	40.303 ±0.97	29.541 ±0.12	17.734 ±0.17	18.708 ±0.08	3.540 ±0.08	3.482 ±0.02	3.149 ±0.02	12.103 ±0.10	3.004 ±0.01	3.659 ±0.03