extract dataparser configs to a stand-alone file, support custom dataparsers (#1909)

* extract dataparser configs to a stand-alone file, support custom dataparsers

* add license

* fix pylint issues

* fix type error issue

* update naming; add documentations;

* print f string

* fix pylint issue

---------

Co-authored-by: Matthew Tancik <tancik@berkeley.edu>

docs/developer_guides/new_methods.md

@@ -16,6 +16,7 @@ We recommend the following file structure:
 │   ├── custom_model.py [optional]
 │   ├── custom_field.py [optional]
 │   ├── custom_datamanger.py [optional]
+│   ├── custom_dataparser.py [optional]
 │   ├── ...
 ├── pyproject.toml
 ```
@@ -76,6 +77,38 @@ Instead, you may use the `NERFSTUDIO_METHOD_CONFIGS` environment variable to tem
 export NERFSTUDIO_METHOD_CONFIGS="my-method=my_method.my_config:MyMethod"
 ```
 
+## Registering custom dataparser with nerfstudio
+We also support adding new dataparsers in a similar way. In order to extend the NeRFstudio and register a customized dataparser, you can register it with Nerfstudio as a `nerfstudio.dataparser_configs` entrypoint in the `pyproject.toml` file. Nerfstudio will automatically look for all registered dataparsers and will register them to be used by methods such as `ns-train`.
+
+You can declare the dataparser in the same config file:
+```python
+"""my_method/my_config.py"""
+
+from nerfstudio.plugins.registry_dataparser import DataParserSpecification
+from my_method.custom_dataparser import CustomDataparserConfig
+
+MyDataparser = DataParserSpecification(config=CustomDataparserConfig)
+```
+
+Then add the following lines in the `pyproject.toml` file, where the entrypoint to the new dataparser is set.
+
+"""pyproject.toml"""
+
+[project]
+name = "my_method"
+
+# ...
+
+[project.entry-points.'nerfstudio.dataparser_configs']
+custom-dataparser = 'my_method.my_config:MyDataparser'
+```
+
+finally run the following to register the dataparser.
+
+```
+pip install -e .
+```
+
 ## Running custom method
 
 After registering your method you should be able to run the method with,