docs: add Python OTLP integration quick-start guide

[databufflabs]

Description

Many Python developers want to connect their applications to DataBuff via OpenTelemetry. Currently there are quick-start guides for Docker and Spring Boot, but not for Python — one of the most popular OTel languages.

Task

Create a new document docs/快速入门/python-otlp-integration.md (and optionally _en.md) that walks through:

1. Starting DataBuff (link to the Docker install guide)
2. Installing the OpenTelemetry Python SDK and OTLP exporter
3. Configuring the OTLP exporter endpoint to the DataBuff ingest endpoint
4. Instrumenting a minimal Python application (e.g., Flask or FastAPI)
5. Verifying traces and metrics appear in the DataBuff UI

Files to create/change

• New file: docs/快速入门/python-otlp-integration.md
• Optionally: docs/快速入门/python-otlp-integration_en.md

Acceptance criteria

• New guide is created with step-by-step instructions
• Includes Python code snippets (e.g., pip install, SDK initialization)
• References existing Docker install docs for DataBuff setup
• Traces/metrics verification steps are included
• Follows the style of the existing spring-boot-otlp-integration.md

Skill requirements

• Python basics
• OpenTelemetry concepts (OTLP exporter)
• Markdown

Resources

• docs/快速入门/spring-boot-otlp-integration.md — existing guide to follow as template
• docs/快速入门/docker安装部署.md — install guide to reference
• docs/opentelemetry-otlp-ingestion.md — OTLP ingestion doc
• OpenTelemetry Python docs: https://opentelemetry.io/docs/languages/python/