Remove SENTRY_DSN from required env vars

Why these changes are being introduced:

For local development, or external users of this application, it does not make sense
to require a SENTRY_DSN environment variable.  While setting this to 'none' would
satisfy the config setup, and not use Sentry, it feels unnecessary.

How this addresses that need:
* Moves SENTRY_DSN to optional env vars in Config class

Side effects of this change:
* SENTRY_DSN is no longer required as an env var, but providing it will still get
picked up used

Relevant ticket(s):
* None

README.md

@@ -66,10 +66,10 @@ WORKSPACE=dev
 RECORD_SKIP_LIST=<oai-pmh-id1> <oai-pmh-id2>
 
 # Sets the interval for logging status updates as records are written to the output file. Defaults to 1000, which will log a status update for every thousandth record.
-STATUS_UPDATE_INTERVAL = 1000
+STATUS_UPDATE_INTERVAL=1000
 
-# If set to a valid Sentry DSN, enables Sentry exception monitoring This is not needed for local development.
-SENTRY_DSN = <sentry-dsn-for-oai-pmh-harvester>
+# If set to a valid Sentry DSN, enables Sentry exception monitoring. This can also be set to 'none'.
+SENTRY_DSN=<sentry-dsn-for-oai-pmh-harvester>
 ```
 
 ## CLI commands

harvester/config.py

@@ -14,8 +14,8 @@
 
 
 class Config:
-    REQUIRED_ENV_VARS = ("WORKSPACE", "SENTRY_DSN")
-    OPTIONAL_ENV_VARS = ("RECORD_SKIP_LIST", "STATUS_UPDATE_INTERVAL")
+    REQUIRED_ENV_VARS = ("WORKSPACE",)
+    OPTIONAL_ENV_VARS = ("RECORD_SKIP_LIST", "SENTRY_DSN", "STATUS_UPDATE_INTERVAL")
 
     def __init__(self, logger: logging.Logger | None = None):
         """Set root logger as default when creating class instance."""

tests/test_config.py

@@ -51,14 +51,6 @@ def test_config_check_required_env_vars_success(config):
     config.check_required_env_vars()
 
 
-def test_config_check_required_env_vars_error(config, monkeypatch):
-    monkeypatch.delenv("SENTRY_DSN")
-    with pytest.raises(
-        OSError, match="Missing required environment variables: SENTRY_DSN"
-    ):
-        config.check_required_env_vars()
-
-
 def test_config_env_var_access_success(config):
     assert config.STATUS_UPDATE_INTERVAL == "1000"