Docs: Fix retrieval of entry points from consumer's `tsconfig.json`

**Describe the bug**
Following up from the conversation [here](https://github.com/ipfs/aegir/pull/1107#issuecomment-1328033031) we should be able to parse the `entryPoints` from a user's `tsconfig.json`

**To Reproduce**
Steps to reproduce the behavior:
1. run ```aegir docs```

**Expected behavior**
If a user has a `tsconfig-docs.aegir.json` we should derive the entryPoints from there.

Run `aegir docs` with a consumer project that has `tsconfig-docs.aegir.json`, then trace how the command discovers entry points from that configuration. Done means the command derives the entryPoints from the consumer's `tsconfig-docs.aegir.json` instead of failing to retrieve them.

Written by the indexing model from the issue text.