Log absolute path of input data in loader

If the data path given to the CLI is a relative path, then the loader logging the input data path will be a _relative path_: https://github.com/DiamondLightSource/httomo/blob/bce8fc7ffd411d22a07dc21c0b4cc090b4dcaa77/httomo/loaders/standard_tomo_loader.py#L220-L223

This means that the `debug.log` file will contain a relative path rather than an absolute one, for example:
```
2024-05-17 17:29:23.555 | INFO | httomo.utils:log_once:54 - Pipeline has been separated into 2 sections
2024-05-17 17:29:23.556 | INFO | httomo.utils:log_once:64 - See the full log file at: /dls/tmp/twi18192/17-05-2024_17_29_14_output/user.log
2024-05-17 17:29:23.556 | INFO | httomo.utils:log_once:56 - Running loader (pattern=projection): standard_tomo...
2024-05-17 17:29:23.573 | DEBUG | httomo.utils:log_once:48 - The full dataset shape is (220, 128, 160)
2024-05-17 17:29:23.573 | DEBUG | httomo.utils:log_once:48 - Loading data: ../httomo/tests/test_data/tomo_standard.nxs
2024-05-17 17:29:23.573 | DEBUG | httomo.utils:log_once:48 - Path to data: entry1/tomo_entry/data/data
2024-05-17 17:29:23.573 | DEBUG | httomo.utils:log_once:48 - Preview: (0:180, 0:128, 0:160)
2024-05-17 17:29:23.573 | DEBUG | httomo.utils:log_once:48 - Data shape is (180, 128, 160) of type uint16
2024-05-17 17:29:23.573 | INFO | httomo.utils:log_once:60 - Finished loader: standard_tomo (httomo) Took 17.09ms
```

This is potentially not ideal for debugging purposes, and logging the absolute path to the input data would perhaps be more informative.