Add log level to zoekt webserver
This MR adds SRC_LOG_LEVEL=info
to zoekt-webserver. This will be quite useful since we'd see server start messages like
$ SRC_LOG_LEVEL=info ./bin/zoekt-webserver -listen :6081
{"SeverityText":"INFO","Timestamp":1704114158190114000,"InstrumentationScope":"server","Caller":"zoekt-webserver/main.go:309","Function":"main.main.func1","Body":"starting server","Resource":{"service.name":"zoekt-webserver","service.instance.id":"m1.local"},"Attributes":{"address":":6081"}}