Make threshold for logging slow requests configurable (#5109)

# What this PR does
Makes SLOW_THRESHOLD_SECONDS configurable from environment variable.
This is to support separate metrics pods as having a different
definition of slow request (10s)

## Which issue(s) this PR closes

Related to [issue link here]

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## Checklist

- [x] Unit, integration, and e2e (if applicable) tests updated
- [x] Documentation added (or `pr:no public docs` PR label added if not
required)
- [x] Added the relevant release notes label (see labels prefixed w/
`release:`). These labels dictate how your PR will
    show up in the autogenerated release notes.

engine/settings/base.py

@@ -8,7 +8,7 @@
 from firebase_admin import credentials, initialize_app
 
 from common.api_helpers.custom_ratelimit import getenv_custom_ratelimit
-from common.utils import getenv_boolean, getenv_integer, getenv_list
+from common.utils import getenv_boolean, getenv_float, getenv_integer, getenv_list
 
 VERSION = "dev-oss"
 SEND_ANONYMOUS_USAGE_STATS = getenv_boolean("SEND_ANONYMOUS_USAGE_STATS", default=True)
@@ -835,7 +835,7 @@ class BrokerTypes:
 JINJA_RESULT_MAX_LENGTH = os.getenv("JINJA_RESULT_MAX_LENGTH", 50000)
 
 # Log inbound/outbound calls as slow=1 if they exceed threshold
-SLOW_THRESHOLD_SECONDS = 2.0
+SLOW_THRESHOLD_SECONDS = getenv_float("SLOW_THRESHOLD_SECONDS", 2.0)
 
 # Email messaging backend
 EMAIL_BACKEND = "django.core.mail.backends.smtp.EmailBackend"