feat: include ucanto server principal did as 'aud' key in /version en…

…dpoint (#309)

Motivation:
* make it easy to discover the ucanto server principal
* unlike [reverted
PR](#305), don't change
`did` property
* because at least `@web3-storage/access` cli expects to be able to
parse that value as a Verifier, which it can only do when the `did` is a
`did:key`

packages/access-api/src/routes/version.js

@@ -7,5 +7,6 @@ export async function version(event, env, ctx) {
     commit: env.config.COMMITHASH,
     branch: env.config.BRANCH,
     did: env.signer.did(),
+    aud: env.config.ucantoServerId.did(),
   })
 }