docs: document all OAuthProviderOptions in README

[mattzcarey]

Summary

• Add accessTokenTTL, allowTokenExchangeGrant, and clientIdMetadataDocumentEnabled to the main config example
• Add new "Protected Resource Metadata (RFC 9728)" section documenting the resourceMetadata option
• Rewrite CIMD section to reflect the opt-in flag added in fix: make CIMD explicitly opt-in via clientIdMetadataDocumentEnabled #158 (two-step enablement: option + compat flag)

Test plan

• npm run check passes (typecheck + 279 tests)
• Review rendered README on GitHub for formatting

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Latest commit: 2227ab1

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npm i https://pkg.pr.new/cloudflare/workers-oauth-provider/@cloudflare/workers-oauth-provider@167

commit: 2227ab1