DEV: Correct typos and spelling mistakes (#12812)

Over the years we accrued many spelling mistakes in the code base. 

This PR attempts to fix spelling mistakes and typos in all areas of the code that are extremely safe to change 

- comments
- test descriptions
- other low risk areas

config/discourse_defaults.conf

@@ -173,7 +173,7 @@ message_bus_redis_skip_client_commands = false
 enable_cors = false
 cors_origin = ''
 
-# enable if you really need to serve assets in prd
+# enable if you really need to serve assets in prod
 serve_static_assets = false
 
 # number of sidekiq workers (launched via unicorn master)
@@ -210,7 +210,7 @@ secret_key_base =
 fallback_assets_path =
 
 # S3 settings used for serving ALL public files
-# be sure to configre a CDN as well per cdn_url
+# be sure to configure a CDN as well per cdn_url
 s3_bucket =
 s3_region =
 s3_access_key_id =
@@ -315,7 +315,7 @@ anon_cache_store_threshold = 2
 # you may restrict it so only specific themes are approved
 # in allowlist mode all theme updates must happen via git repos
 # themes missing from the list are automatically disallowed
-# list is a comma seperated list of git repos eg:
+# list is a comma separated list of git repos eg:
 # https://github.com/discourse/discourse-custom-header-links.git,https://github.com/discourse/discourse-simple-theme.git
 allowed_theme_repos =