docs: add docstrings to DocumentConverter #2748 (#2782)

* docs: add docstrings for DocumentConverter

Signed-off-by: Julia Pap <papjuli@gmail.com>

* Apply suggestions from code review

Improve docstrings in DocumentConverter

Co-authored-by: Cesar Berrospi Ramis <75900930+ceberam@users.noreply.github.com>
Signed-off-by: Julia Pap <papjuli@gmail.com>

* docs: improve docstring formatting and wording in DocumentConverter

* docs: show init method in document converter reference

* docs: change back indents to 4x in DocumentConverter docstrings

griffe was issuing warnings of confusing indentation

* docs: clarify `max_num_pages` and `page_range` args in `DocumentConverter` methods

* docs: fix some Yields and Returns in DocumentConverter docstrings

* DCO Remediation Commit for Julia Pap <papjuli@gmail.com>

I, Julia Pap <papjuli@gmail.com>, hereby add my Signed-off-by to this commit: cf2ea4e0f0ef5b65a3dd32a982f4465eac2cd3a8
I, Julia Pap <papjuli@gmail.com>, hereby add my Signed-off-by to this commit: 57446af16829d9a203581a3e87a18c630dd4159d
I, Julia Pap <papjuli@gmail.com>, hereby add my Signed-off-by to this commit: 5d613edb8cbf3bd132a2cf75e3a4b9bba36d5697
I, Julia Pap <papjuli@gmail.com>, hereby add my Signed-off-by to this commit: b195281f565a219c5e1e6f529779285c44439d2f
I, Julia Pap <papjuli@gmail.com>, hereby add my Signed-off-by to this commit: 5d4a3af5d5401c4f4d2599aa3341b4391de68a78

Signed-off-by: Julia Pap <papjuli@gmail.com>

* docs: ignore init description, rephrased docstrings

Signed-off-by: Cesar Berrospi Ramis <ceb@zurich.ibm.com>

---------

Signed-off-by: Julia Pap <papjuli@gmail.com>
Signed-off-by: Cesar Berrospi Ramis <ceb@zurich.ibm.com>
Co-authored-by: Cesar Berrospi Ramis <75900930+ceberam@users.noreply.github.com>
Co-authored-by: Cesar Berrospi Ramis <ceb@zurich.ibm.com>