Provide more details in `greta_sitrep()` to assist with debugging

[njtierney]

• R & Rstudio version
• Greta version - and point to whether installed from CRAN/github etc.
• Paths to Python, TF, and TFP. This might help debug issues with this
• Paths to greta env (if used)
• Note if greta env is used
• Don't just print TF/TFP versions, list where they are installed
• List python version, and where it is installed, which environment is used
• Add various helper functions to identify where TF is installed
• Add various helper functions to identify where TFP is installed

[njtierney]

See

• https://github.com/r-lib/devtools/blob/6d6ebabc27d882e84a1fd93f900b55a49ccfddf3/R/sitrep.R
• https://github.com/r-lib/usethis/blob/1f6d511cda0960f9edd0d822b9906214b45681f5/R/sitrep.R

[njtierney]

Check if current versions of TF/TFP are the latest version - suggest updating them if they are later.

[njtierney]

Suggest reinstall_greta_deps() if things don't work?