Adjust raft constants for long running tests

Summary:
Based on the recent builds (https://apollo.memgraph.io/runs/642045/,
https://apollo.memgraph.io/runs/642700/ https://apollo.memgraph.io/runs/640896/
https://apollo.memgraph.io/runs/640538/) `ha` stress tests fail.

Every tests that failed, has a re-election in progress. I'm bumping election
timeout constatns in order to give the cluster more time to do what it needs to
do before going in the state where it fails.

Reviewers: ipaljak

Reviewed By: ipaljak

Subscribers: pullbot

Differential Revision: https://phabricator.memgraph.io/D2292

tests/stress/raft.json

@@ -1,7 +1,7 @@
 {
-  "election_timeout_min": 750,
-  "election_timeout_max": 1000,
-  "heartbeat_interval": 100,
+  "election_timeout_min": 1200,
+  "election_timeout_max": 1500,
+  "heartbeat_interval": 200,
   "replication_timeout": 10000,
-  "log_size_snapshot_threshold": 500
+  "log_size_snapshot_threshold": 2500
 }