404 Fixes and API key updates

[harishkotra]

Following updates have been made as part of this PR:

1. Updated code snippets to show API key usage in the https://docs.gaianet.ai/agent-integrations/intro page.
2. Fixed 404 issues in the https://docs.gaianet.ai/getting-started/system-requirements/ page & updated redirects in the docusaurs setup.
3. Updated API Key usage references in the https://docs.gaianet.ai/getting-started/api-reference cURL commands.

[juntao]

Hello, I am a PR summary agent on flows.network. Here are my reviews of code commits in this PR.

---

Commit 3e4a7af63903c54f243942e3d356a53d7d415f25

Key Changes:

1. API Key Placeholder Updates: Replaced YOUR_API_KEY_GOES_HERE with clear instructions and examples to replace it with the user's own API key in multiple documentation files.
2. Authentication Tutorial Links: Added links to an authentication tutorial for obtaining an API key where applicable.
3. 404 Fixes: Updated redirection rules in docusaurus.config.js to fix broken links, particularly addressing /getting-started/quick-start/system-requirements and additional paths.

Most Important Findings:

• API Key Security: Ensured that all documentation clearly instructs users to replace placeholder API keys with their own, enhancing security.
• Link Corrections: Fixed several 404 errors by correcting URL redirections in the Docusaurus configuration.