Settings-overrides in settings.php are not respected

Configuration values are stored in `config/sync/gdx_analytics_drupal_snowplow.settings.yml`, and look like this:
```
_core:
default_config_hash: UFNo1YN6FHNzJZ0Sqq2zRrQ1yWgOyH_537Ek5qcBuqg
gdx_collector_mode: spt.apps.gov.bc.ca
gdx_analytics_snowplow_version: 1
gdx_analytics_snowplow_script_uri: 'https://www2.gov.bc.ca/StaticWebResources/static/sp/sp-2-14-0.js'
gdx_analytics_app_id: Snowplow_standalone
gdx_analytics_search_path: /search
gdx_analytics_search_key: keys
```

However, Drupal's config system is set up such that you can choose to override settings values in your site's `settings.php` file, with a line like this:
```
/**
* Snowplow override
*/
$config['gdx_analytics_drupal_snowplow.settings']['gdx_collector_mode'] = '';
```

Currently, this override mechanism is unable to work, because the settings are being retrieved using `getRawData()` rather than `get()`. I think that `getRawData()` is intended for lower-level manipulations, because it gets the data directly from the config storage system, before any overrides have been applied.

A quick search through the contrib modules installed for our current project appears to confirm this -- "get()" is generally what is used for config values retrieval.

Search the module for the configuration retrieval that currently calls getRawData(), using config/sync/gdx_analytics_drupal_snowplow.settings.yml as the setting reference. Read the surrounding configuration access and verify behavior with a settings.php override for gdx_collector_mode. Done means the override value is respected rather than the stored YAML value.

Written by the indexing model from the issue text.