Distinguish updates

[iilyak]

Overview

This PR allow us to distinguish between new doc and update of the existent doc for tracing.

Testing recommendations

1. update rel/overlay/etc/default.ini as follows

rel/overlay/etc/default.ini
[tracing]
enabled = true ; true | false
app_name = couchdb ; value to use for the `location.application` tag
protocol = http ; udp | http - which reporter to use
endpoint = http://127.0.0.1:14268
 
[tracing.filters]
all = (#{}) -> true

2. start jaeger in docker container

docker run -d -p 6831:6831/udp -p 16686:16686 -p 14268:14268 jaegertracing/all-in-one:1.14

3. Start couchdb dev/run --admin=adm:pass --no-join
4. Create database curl -X PUT -u adm:pass http://127.0.0.1:15984/test
5. Create document curl -X PUT -u adm:pass http://127.0.0.1:15984/test -H Content-Type:application/json -d '{"_id":"doc1"}'
6. Update document curl -X PUT -u adm:pass "http://127.0.0.1:15984/test/doc1?rev=8-4f98b201f7a6f147a952fe70651f0a95" -H Content-Type:application/json -d '{"_id":"doc1","val": 4}'
7. Update document curl -X PUT -u adm:pass "http://127.0.0.1:15984/test/doc1" -H Content-Type:application/json -d '{"_id":"doc1","dfd": 4, "_rev": "11-fdcab8b70c87eb64255f504a5d983ab0"}'
8. Open http://localhost:16686/ in the browser and search for spans (you should find some traces)
   • the first event should have action equal to db.doc.write
   • the second event should have action equal to db.doc.update
   • the third event should have action equal to db.doc.update

Related Issues or Pull Requests

N/A

Checklist

• [x] Code is written and works correctly
• [ ] Changes are covered by tests
• [ ] Any new configurable parameters are documented in rel/overlay/etc/default.ini
• [ ] A PR for documentation changes has been made in https://github.com/apache/couchdb-documentation