docs: Add a new Trinsic Platform Walkthrough

[lucasamonrc]

This PR adds the platform walkthrough to our documentation website. It also adds small navigation updates with the intent to make certain pages more discoverable.

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PR-Codex overview

This PR focuses on updating the documentation and adding new content related to the Trinsic platform.

Detailed summary

• Added a section on how to send yourself a credential using the Credential Handler API.
• Updated the navigation menu and links in the index.md file.
• Added a platform walkthrough guide.
• Added a section on creating an ecosystem in the platform walkthrough guide.
• Added a section on accessing the White Label Wallet in the platform walkthrough guide.
• Added a section on creating a verifiable credential template in the platform walkthrough guide.
• Added a section on registering an issuer in the platform walkthrough guide.
• Added a section on issuing a credential in the platform walkthrough guide.

The following files were skipped due to too many changes: docs/guide/platform-walkthrough.md

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[github-actions]

Preview docs site for docs/platform-walkthrough@5499a04d
Changed paths:

1. docs/guide/issuance.md
2. docs/guide/platform-walkthrough.md
3. docs/index.md
4. docs/reference/proto/index.md