feat: access-api version route sets did=ucantoServerId and adds a sig…

…ner prop (#305)

Motivation:
* `@web3-storage/access` cli expects to be able to fetch /version and
pull the `did` property in order to create the ucanto Verifier that is
used as the `aud` when signing ucans
*
https://github.com/web3-storage/w3protocol/blob/main/packages/access-client/src/cli/utils.js#L28
* before this change, that `did` property came from `ctx.signer`, which
will have a `did:key`.
* but since #303 , the
verifier used in the ucanto server for upload-api is actually different
than `ctx.signer.did()`. So this PR makes it so /version `did` property
actually comes from `ctx.config.ucantoServerId`
* it also adds a new key to that endpoint, `signer`, which is the public
key of the signer (which now can be different than the `DID` of the
ucanto server id). I added this just in case someone wants to use the
/version endpoint to know the undelrying signer pubkey

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

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