fix: ensure UTF-8 encoding when reading text files in ingestion helper

[akshayjalluri6]

Description

This PR ensures that text files are read using UTF-8 encoding in the _load_file_to_documents method of the ingestion helper. Previously, the encoding was not explicitly specified, which could lead to issues when handling files with non-UTF-8 encodings.

Motivation:

• Explicitly specifying UTF-8 encoding improves the robustness of file ingestion, ensuring consistent behavior across various environments and file types.
• Prevents potential errors when handling text files with special characters or encodings that default to non-UTF-8.
• This way PrivateGPT can process any language files.

Relevant Context:

• This change affects how files are read when no specific file reader is found for a given file extension.
• No dependencies were introduced for this change.

---

Type of Change

• ✅ Bug fix (non-breaking change which fixes an issue)

---

How Has This Been Tested?

1. Code Inspection:

   • Verified that the change explicitly specifies UTF-8 encoding in the read_text method.
   • Ensured the updated method still adheres to the expected behavior for all file types.

2. Unit Testing:

   • Ran existing unit tests to confirm no regressions were introduced.
   • Verified that files with UTF-8 encoding and special characters are read correctly without errors.

3. Manual Testing:

   • Tested the ingestion of text files containing special characters (e.g., emojis, non-ASCII text) to confirm proper handling.
   • Confirmed no issues when processing files of other formats or extensions.

Test Configuration:

• OS: Windows-11
• Python Version: 3.11.9

---

Checklist

• ✅ My code follows the style guidelines of this project.
• ✅ I have performed a self-review of my code.
• ✅ I have commented my code, particularly in hard-to-understand areas.
• ✅ My changes generate no new warnings.
• ✅ I have added tests that prove my fix is effective or that my feature works.
• ✅ New and existing unit tests pass locally with my changes.
• ✅ I ran make check; make test to ensure mypy and tests pass.

---

This structure clearly outlines the change, why it was made, and how it was tested. Let me know if you need further adjustments!