feat: Allow users to set json log output

[NoUseFreak]

Add -format=json options to allow logging in json format.

{"time":"2023-11-04T11:17:26.702372+01:00","level":"INFO","msg":"Using '/workdir/tusd/data' as directory storage."}
{"time":"2023-11-04T11:17:26.702557+01:00","level":"INFO","msg":"Using 0.00MB as maximum size."}
{"time":"2023-11-04T11:17:26.702594+01:00","level":"INFO","msg":"Supported tus extensions: creation,creation-with-upload,termination,concatenation,creation-defer-length"}
{"time":"2023-11-04T11:17:26.7026+01:00","level":"INFO","msg":"Using 0.0.0.0:8080 as address to listen."}
{"time":"2023-11-04T11:17:26.702603+01:00","level":"INFO","msg":"Using /files/ as the base path."}
{"time":"2023-11-04T11:17:26.702631+01:00","level":"INFO","msg":"Using /metrics as the metrics path."}
{"time":"2023-11-04T11:17:26.702947+01:00","level":"INFO","msg":"You can now upload files to: http://[::]:8080/files/"}

[Acconut]

Thank you for the PR!

[Acconut]

Thank you for the PR! I has been merged in 9b6ada9 🎉 I apologize that your authorship of this commit got lost when I added a commit locally and squashed them together.