Images that are not in the `./assets` dir should also be exported

[dr-dr_xp]

Images that are not in the ./assets dir should also be exported.

Create a file outside pages, referencing an image outside assets:

workspace/
▸ assets/
▸ journals/
▸ logseq/
▸ pages/
▾ tips/
  ▾ approx-combination/
       binomial-normal-margin.png
    approx-combination.md

Content of approx-combination.md:

![foo](approx-combination/binomial-normal-margin.png)

It’s all right when editing and rendering.

But the Image does not display in the exported graph

After exporting with top-right menu -> export graph -> export public pages, the image disappears.

There are two problems with it:

1. Images not in the assets dir are not exported. My image is tips/approx-combination/binomial-normal-margin.png, but in the output dir there is no such file.

2. The URL is truncated. which can be found in the exported index.html:

   ...![foo](approx-combination/binomial-normal-margin.png)...
   

   But when opening it in a browser, the file path is truncated:

   <img loading="lazy" src="pprox-combination/binomial-normal-margin.png" title="foo" class="rounded-sm shadow-xl relative" style="display: none;">