[SQLite-kit] Support custom base API URL for d1-http

[GoodGoodJM]

The d1-http driver has the Cloudflare API base URL hardcoded. Wrangler supports overriding this via CLOUDFLARE_BASE_API_URL but drizzle-kit has no equivalent, so custom endpoints like proxies or testing environments can't be used.

Added an optional baseApiUrl field to d1-http credentials. Falls back to https://api.cloudflare.com/client/v4 when not specified.

// drizzle.config.ts
export default defineConfig({
  dialect: 'sqlite',
  driver: 'd1-http',
  dbCredentials: {
    accountId: '...',
    databaseId: '...',
    token: '...',
    baseApiUrl: 'https://custom.endpoint.com/client/v4', // optional
  },
});