Issues with defining links when using the to_rst and to_md filters

I am the author of the [ansible-doc-template-extractor](https://pypi.org/project/ansible-doc-template-extractor/) package which uses the `to_rst` and `to_md` Jinja2 filters of this repo.

These filters do such a thorough job in [escaping](https://github.com/ansible-community/antsibull-docs-parser/blob/main/src/antsibull_docs_parser/rst.py#L24) that it is basically impossible to create a link in the filter input text that survives as a link.

Examples for input text and output text for the `to_rst` filter:
```
Input to_rst output
------------------------------------------------------------------------------------------------------
:ref:`my_ref_target` :ref:\`my\_ref\_target\`
`my ref target <../myfile.html#my-ref-target>`_ \`my ref target \<../myfile.html#my-ref-target\>\`\_
|my_ref_target| \|my\_ref\_target\|
```

Can we please have some support for defining links using RST syntax using `:ref:` and MD link syntax `[]()`?

I can think of the following options:

* Option 1: Always allow these links in [postprocess_rst_paragraph()](https://github.com/ansible-community/antsibull-docs-parser/blob/main/src/antsibull_docs_parser/rst.py#L361) and [postprocess_md_paragraph()](https://github.com/ansible-community/antsibull-docs-parser/blob/main/src/antsibull_docs_parser/md.py#L104)
* Option 2: Add an optional parameter on the `to_rst` and `to_md` filters that specifies a string with the characters that should not be escaped.
* Option 3: Add an optional parameter on the `to_rst` and `to_md` filters that specifies a custom `postprocess_paragraph()` function, replacing the default one (or in addition to the default one).
* Option 4: Some Ansible-style way of linking to RST targets or MD headings.

What do you think about this?

Start by reading postprocess_rst_paragraph() in antsibull_docs_parser/rst.py and postprocess_md_paragraph() in antsibull_docs_parser/md.py, then trace how the to_rst and to_md filters invoke them. Compare the proposed RST and Markdown link forms and determine a clear supported behavior; done means links survive filtering without breaking the existing escaping behavior.

Written by the indexing model from the issue text.