Reduce support cases: Node.js versioning

The most common support case we see is related to missing or incorrect Node.js version config. Definitely a known pain point and not easy to solve. We have some docs on Node.js versioning [here](https://learn.microsoft.com/en-us/azure/azure-functions/functions-reference-node?tabs=javascript%2Clinux%2Cazure-cli&pivots=nodejs-model-v4#node-version).

## Support cases from June 2023 - Sept 2023

_Internal-only links_:

Missing WEBSITE_NODE_DEFAULT_VERSION:
- https://elixir.microsoft.com/case-review/2307280040007716
- https://elixir.microsoft.com/case-review/2309040030003949
- https://elixir.microsoft.com/case-review/2309040050003658
- https://elixir.microsoft.com/case-review/2309210030004197
- https://elixir.microsoft.com/case-review/2306060030004519

Confused about WEBSITE_NODE_DEFAULT_VERSION vs linuxFxVersion:
- https://elixir.microsoft.com/case-review/2305290050001976

Bad linuxFxVersion:
- https://elixir.microsoft.com/case-review/2308070050000149
- https://elixir.microsoft.com/case-review/2308140030003966
- https://elixir.microsoft.com/case-review/2308170010016847
- https://elixir.microsoft.com/case-review/2308180010002626

Mismatched host version and linuxFxVersion:
- https://elixir.microsoft.com/case-review/2306270040003485

Troubles upgrading from v14 to v18
- https://elixir.microsoft.com/case-review/2307150040000583
- https://elixir.microsoft.com/case-review/2308280040014730
- https://elixir.microsoft.com/case-review/2306190030004261