Increase default SIDEKIQ_MEMORY_KILLER_MAX_RSS to 2GB

There are many warnings like below
recorded in {GITLAB_LOG_DIR}/supervisord/sidekiq.log.
This can be avoided by simply increasing SIDEKIQ_MEMORY_KILLER_MAX_RSS.

----
{
  "severity": "WARN",
  "time": "[MASKED]",
  "class": "Gitlab::SidekiqDaemon::MemoryKiller",
  "pid": [MASKED],
  "message": "Sidekiq worker RSS out of range",
  "current_rss": 1009636,
  "soft_limit_rss": 1000000,
  "hard_limit_rss": [MASKED],
  "memory_total_kb": [MASKED],
  "reason": "current_rss(1009636) \u003e soft_limit_rss(1000000)",
  "running_jobs": [],
  "retry": 0
}
----

For sameersbn/gitlab, this parameter have been introduced with
following commit on May 21, 2015 and never updated until today:
e4008cc

On upstream, the default setting documentation is updated here:
  https://gitlab.com/gitlab-org/gitlab-foss/-/merge_requests/31682
but it is said "the documentation is outdated" at this time.
I could not find out when the value is increased.

At least, In omnibus-gitlab, this have been introduced in MR 2360
(release 11.10.0+ce.0 / 11.10.0+ee.0)
https://gitlab.com/gitlab-org/omnibus-gitlab/-/merge_requests/2360

Author: kkimurak

README.md

@@ -1746,7 +1746,7 @@ Timeout for sidekiq shutdown. Defaults to `4`
 
 ##### `SIDEKIQ_MEMORY_KILLER_MAX_RSS`
 
-Non-zero value enables the SidekiqMemoryKiller. Defaults to `1000000`. For additional options refer [Configuring the MemoryKiller](http://doc.gitlab.com/ce/operations/sidekiq_memory_killer.html)
+Non-zero value enables the SidekiqMemoryKiller. Defaults to `2000000`. For additional options refer [Configuring the MemoryKiller](http://doc.gitlab.com/ce/operations/sidekiq_memory_killer.html)
 
 ##### `GITLAB_SIDEKIQ_LOG_FORMAT`
 

assets/runtime/env-defaults

@@ -62,7 +62,7 @@ REDIS_DB_NUMBER=${REDIS_DB_NUMBER:-0}
 ## SIDEKIQ
 SIDEKIQ_SHUTDOWN_TIMEOUT=${SIDEKIQ_SHUTDOWN_TIMEOUT:-4}
 SIDEKIQ_CONCURRENCY=${SIDEKIQ_CONCURRENCY:-25}
-SIDEKIQ_MEMORY_KILLER_MAX_RSS=${SIDEKIQ_MEMORY_KILLER_MAX_RSS:-1000000}
+SIDEKIQ_MEMORY_KILLER_MAX_RSS=${SIDEKIQ_MEMORY_KILLER_MAX_RSS:-2000000}
 GITLAB_SIDEKIQ_LOG_FORMAT=${GITLAB_SIDEKIQ_LOG_FORMAT:-json}
 
 ## PUMA