chore: rectify orthographic errors in NLU data, API specs, and documentation

[28ananthaprakash]

Proposed changes:
This PR performs a codebase-wide audit to resolve typographic and orthographic inconsistencies. The changes target multiple distinct areas of the repository to ensure higher quality standards and searchability.

Scope of Changes

• NLU Training Data (sara_nlu_data.yml): Corrected syntax in training examples to ensure dataset integrity.
• OpenAPI Specifications (action_server.yml, rasa.yml): Fixed spelling errors within schema descriptions to ensure accurate API documentation generation.
• Source Code (test.py): Rectified typos in docstrings and return value descriptions to improve code maintainability.
• Documentation & Changelogs: Resolved miscellaneous errors in CHANGELOG.mdx and README files for better readability.

Status (please check what you already did):

• added some tests for the functionality
• updated the documentation
• updated the changelog (please check changelog for instructions)
• reformat files using black (please check Readme for instructions)

[CLAassistant]

All committers have signed the CLA.