Add feature for enabling json logging

[lemmus-org]

Allows configuring log output to be json formatted when built using the json-log feature.

For example:

• cargo run

2023-07-03T03:52:43.045692Z  INFO lemmy_db_schema::utils: Running Database migrations (This may take a long time)...
2023-07-03T03:52:43.047078Z  INFO lemmy_db_schema::utils: Database migrations complete.
2023-07-03T03:52:43.083464Z  INFO lemmy_server::code_migrations: Running user_updates_2020_04_02
2023-07-03T03:52:43.084804Z  INFO lemmy_server::code_migrations: 0 person rows updated.
2023-07-03T03:52:43.085039Z  INFO lemmy_server::code_migrations: Running community_updates_2020_04_02
2023-07-03T03:52:43.085850Z  INFO lemmy_server::code_migrations: 0 community rows updated.
2023-07-03T03:52:43.085964Z  INFO lemmy_server::code_migrations: Running post_updates_2020_04_03
2023-07-03T03:52:43.086656Z  INFO lemmy_server::code_migrations: 0 post rows updated.
2023-07-03T03:52:43.086765Z  INFO lemmy_server::code_migrations: Running comment_updates_2020_04_03
2023-07-03T03:52:43.088325Z  INFO lemmy_server::code_migrations: 0 comment rows updated.
2023-07-03T03:52:43.088440Z  INFO lemmy_server::code_migrations: Running private_message_updates_2020_05_05
2023-07-03T03:52:43.088873Z  INFO lemmy_server::code_migrations: 0 private message rows updated.
2023-07-03T03:52:43.088975Z  INFO lemmy_server::code_migrations: Running post_thumbnail_url_updates_2020_07_27
2023-07-03T03:52:43.089405Z  INFO lemmy_server::code_migrations: 0 Post thumbnail_url rows updated.
2023-07-03T03:52:43.089514Z  INFO lemmy_server::code_migrations: Running apub_columns_2021_02_02
2023-07-03T03:52:43.090065Z  INFO lemmy_server::code_migrations: Running instance_actor_2021_09_29
2023-07-03T03:52:43.093276Z  INFO lemmy_server::code_migrations: Running regenerate_public_keys_2022_07_05
2023-07-03T03:52:43.093989Z  INFO lemmy_server::code_migrations: Running initialize_local_site_2022_10_10

• cargo run --feature json-log

{"timestamp":"2023-07-03T03:48:47.630411Z","level":"INFO","fields":{"message":"Running Database migrations (This may take a long time)..."},"target":"lemmy_db_schema::utils"}
{"timestamp":"2023-07-03T03:48:48.433914Z","level":"INFO","fields":{"message":"Database migrations complete."},"target":"lemmy_db_schema::utils"}
{"timestamp":"2023-07-03T03:48:48.471113Z","level":"INFO","fields":{"message":"Running user_updates_2020_04_02"},"target":"lemmy_server::code_migrations"}
{"timestamp":"2023-07-03T03:48:48.472628Z","level":"INFO","fields":{"message":"0 person rows updated."},"target":"lemmy_server::code_migrations"}
{"timestamp":"2023-07-03T03:48:48.472864Z","level":"INFO","fields":{"message":"Running community_updates_2020_04_02"},"target":"lemmy_server::code_migrations"}
{"timestamp":"2023-07-03T03:48:48.473765Z","level":"INFO","fields":{"message":"0 community rows updated."},"target":"lemmy_server::code_migrations"}
{"timestamp":"2023-07-03T03:48:48.473887Z","level":"INFO","fields":{"message":"Running post_updates_2020_04_03"},"target":"lemmy_server::code_migrations"}
{"timestamp":"2023-07-03T03:48:48.474783Z","level":"INFO","fields":{"message":"0 post rows updated."},"target":"lemmy_server::code_migrations"}
{"timestamp":"2023-07-03T03:48:48.474913Z","level":"INFO","fields":{"message":"Running comment_updates_2020_04_03"},"target":"lemmy_server::code_migrations"}
{"timestamp":"2023-07-03T03:48:48.476622Z","level":"INFO","fields":{"message":"0 comment rows updated."},"target":"lemmy_server::code_migrations"}
{"timestamp":"2023-07-03T03:48:48.476728Z","level":"INFO","fields":{"message":"Running private_message_updates_2020_05_05"},"target":"lemmy_server::code_migrations"}
{"timestamp":"2023-07-03T03:48:48.477190Z","level":"INFO","fields":{"message":"0 private message rows updated."},"target":"lemmy_server::code_migrations"}
{"timestamp":"2023-07-03T03:48:48.477305Z","level":"INFO","fields":{"message":"Running post_thumbnail_url_updates_2020_07_27"},"target":"lemmy_server::code_migrations"}
{"timestamp":"2023-07-03T03:48:48.477748Z","level":"INFO","fields":{"message":"0 Post thumbnail_url rows updated."},"target":"lemmy_server::code_migrations"}
{"timestamp":"2023-07-03T03:48:48.477855Z","level":"INFO","fields":{"message":"Running apub_columns_2021_02_02"},"target":"lemmy_server::code_migrations"}
{"timestamp":"2023-07-03T03:48:48.478434Z","level":"INFO","fields":{"message":"Running instance_actor_2021_09_29"},"target":"lemmy_server::code_migrations"}
{"timestamp":"2023-07-03T03:48:48.482569Z","level":"INFO","fields":{"message":"Running regenerate_public_keys_2022_07_05"},"target":"lemmy_server::code_migrations"}
{"timestamp":"2023-07-03T03:48:48.483338Z","level":"INFO","fields":{"message":"Running initialize_local_site_2022_10_10"},"target":"lemmy_server::code_migrations"}

Using structured logging can be really helpful for analysis, especially when ingested by 3rd-party tools. They can auto-detect the fields allowing you to easily search or generate metrics/alerts based on values.