Add general documentation for package.

Update code-docstring for execute_nlp_pipeline() and other functions in the NLP script.

"""Returns the cleaned version of the annotation label after performing the following steps:

```python
remove_whitespaces()
expand_word_contractions()
replace_special_chars()
convert_number_to_word()
make_lowercase()
get_root_word()
```

Args:
    input_label (str): Input annotation label text.

Returns:
    str: Cleaned version of the annotation label text.
"""

Improve get_asctb_data_url() to also pull out gid from the Sheet-Config data on line 59, to make code more modular.
Update fetch_ct_info_from_asctb_google_sheet() line 88 to also include '&gid=0129321849sdkj00329'.

Work completed up till now:

1. Azimuth Kidney --> ASCTB Kidney v1.2:

Translations verified by Sanjay Jain and Ellen Q.

2. Azimuth Lung HLCAv2 --> ASCTB Lung v1.2

Translations verified by Gloria Pryhuber

3. Azimuth Heart --> ASCTB Heart v1.2

Translations verified by Marc Halushka

Next-steps:

a. Confirm with Katy and Ellen which crosswalks to focus on. Brief discussion was about Azimuth's other reference organs, CellTypist organs, and PopV/Tabula Sapiens organs.
b. Confirm if we need all organ-datasets from CellTypist and PopV/Tabula Sapiens mapped to ASCTB using this package?
c. Souradeep to operationalize this package into a data-pipeline with potential for CICD.
d. Future feature request - Add logic to also consider gene-expression profiles (biomarkers from query-dataset) mapped to ASCTB canonical markers, in order to make a more reliable cross-dataset translation mapping.