feat/chunking by page

[saeedesmaili]

It's nice that we have the option to chunk by title, and the multipage_sections=False allows us to consider a page break as a new chunk.

But it would be great to have the option to only chunk by page. So if we have a document as following:

[page 1]
## title
text

## title 2
text
[page 2]
## title 3
text

The chunking by page would split the above document into two chunks (one chunk for each page). I believe it is not possible to achieve this currently.