Introduce more context to logging

[ross-spencer]

A new log formatter is introduced that adds program contex to the log output, e.g. source file, and line of code where a log call is made. Additional program context can be added consistently. Datetime is formatted in ISO format and an option is provided to use UTC or local timezones.

Log formatting now looks more like as follows:

r0ss@exponential-decay:~/git/richardlehane/siegfried/cmd/roy$ ./roy harvest
2024-08-03 13:26:06 :: roy :: roy.go:658: roy: errors saving reports to disk [open : no such file or directory]

r0ss@exponential-decay:~/git/richardlehane/siegfried/cmd/roy$ ./roy build
2024-08-03 13:32:20 :: roy :: roy.go:658: pronom: error loading containers; got open : no such file or directory
Unless you have set `-nocontainer` you need to download a container signature file

r0ss@exponential-decay:~/git/richardlehane/siegfried/cmd/sf$ ./sf
2024-08-03 13:37:10 :: sf :: sf.go:477: [FATAL] expecting one or more file or directory arguments (or '-' to scan stdin)

versus;

r0ss@exponential-decay:~/git/richardlehane/siegfried/cmd/sf$ ./sf
2024/08/03 15:49:38 [FATAL] expecting one or more file or directory arguments (or '-' to scan stdin)

r0ss@exponential-decay:~/git/richardlehane/siegfried/cmd/roy$ ./roy build
2024/08/03 15:49:29 pronom: error loading containers; got open : no such file or directory
Unless you have set `-nocontainer` you need to download a container signature file

In future commits, log messages can be modified to remove manually entered references to "roy" or "sf".

One question might be to set datetime to UTC by default or not. I've started using the former in most codebases. Folks may still prefer local.

[richardlehane]

thanks Ross I'll take a look!