Improvements to global_time_series

A few minor and misc improvements for the global_time_series tasks. I may add more over time.

- Use unbuffered output (-u) for

https://github.com/E3SM-Project/zppy/blob/f12bd6fed92d82b223aaa4b8d3744f77f394f3db/zppy/templates/global_time_series.bash#L47

- Move and rename aux sub-directories (global_time_series_*_dir, global_time_series_*_results) somewhere under

`post/analysis/global_time_series`

- Currently, the ocean time series files appear to be recomputed every time if a user wants plots for the entire period. Either add a new option, or (better) automatically determine which files need to be computed.

Start with the linked global_time_series.bash template at line 47 and inspect the post/analysis/global_time_series layout. The requested work covers unbuffered output, relocating auxiliary directories, and preventing unnecessary ocean time-series recomputation; completion should address each item and preserve the task's plotting behavior.

Written by the indexing model from the issue text.