Substitute artefact for fontawesome-icon-defs.js

With an updated config of Staging, the docs-site/scripts/populate-icon-defs.js
is failing on Github CI with OOM errors having outgrown its
configured heap.

```
<--- Last few GCs --->

[7869:0x35b68000]    22861 ms: Mark-Compact 4066.3 (4144.0) -> 4066.3 (4144.0) MB, pooled: 2 MB, 12.63 / 0.00 ms  (average mu = 0.714, current mu = 0.121) allocation failure; scavenge might not succeed
[7869:0x35b68000]    22875 ms: Mark-Compact 4067.0 (4144.7) -> 4067.0 (4144.7) MB, pooled: 2 MB, 12.54 / 0.00 ms  (average mu = 0.579, current mu = 0.121) allocation failure; scavenge might not succeed

<--- JS stacktrace --->

FATAL ERROR: Reached heap limit Allocation failed - JavaScript heap out of memory
```

Adding to Github CI this config:

+      env:
+        NODE_OPTIONS: --max_old_space_size=4096

Changed the Mark-Compact details from the error-message message above from ~2000 to ~4000.

It looks like there is an issue, perhaps *triggered* by the latest staging
config, but with the memory usage of the script.

Locally increasing to `--max_old_space_size=8192` does indeed work.

By adding this artefact to the default, it means that:

* Current builds with `populate-icons: false` will get *a subset* of icons they did not previously. That's only the `archive` server.
* Adding `populate-icons: false` to the Staging config would have it render successfully, at the cost of having to update the file manually down the line.
* This gives us a mitigation if Production build also starts to fail.

We could then:

* fix the memory issue / replace the script with one that produces the same output
* invoke @mojavelinux to see if there are newer best-practices to solve the icon issue.

Author: osfameron