Add OpenAPI spec

[peterjan]

This PR adds an OpenAPI spec for walletd. I'm going to do the same for walletd and hostd. This is in reference to one of the goals we set last year, but we failed to accomplish it in due time. But better late than never.

I'm not too familiar with Scalar, I copy pasted the workflow from indexd and tweaked it a bit. The openapi spec was generated of course, I verified it manually though and ran it through a validator.

Fixes #273

[peterjan]

merge blocker: should add SCALAR_API_KEY secret

[Copilot]

Pull Request Overview

This PR adds an OpenAPI specification for the explored API to enable better documentation and API client generation. The specification includes comprehensive endpoint definitions, schema definitions, and authentication details for the Sia blockchain explorer API.

Key Changes:

• Added complete OpenAPI 3.0 specification defining all explored API endpoints and data structures
• Configured GitHub workflows for automated OpenAPI documentation publishing and version synchronization
• Integrated with Scalar for hosted API documentation

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
openapi.yml	Complete OpenAPI specification for explored API with endpoints, schemas, and authentication
.github/workflows/openapi-sync.yml	Workflow to sync OpenAPI versions on releases
.github/workflows/openapi-publish.yml	Workflow to publish OpenAPI docs to Scalar registry

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[n8mgr]

@codex

[alexfreska]

@peterjan iirc SCALAR_API_KEY is available org wide.