Add API to allow reading & writing history to file

[jeanbaptistelab]

Implement bash history-like feature in Slash: commands will be saved on disk and read when calling the new Slash API (slash_init_history_from_file)
There will be a counter-part in CSH that uses this new feature once this PR is merged.

[Lykkeberg]

This is a neat feature. We have to remember that the CSH can be used in a lot of different contexts at the same time, so if this is going to be extra, super smart, I think we should name the history files with some context information along side the placement of where it has been invoked. But I'm not fully aware of how 🫣

[Lykkeberg]

These history files could also potentially end up containing sensitive information to some customers, so how do we protect that? If say, a command to VM is being entered with a password, then this would be forever locked into a history file. I'm not sure that is a problem or not, but it is something we need to consider.

[jeanbaptistelab]

This is a neat feature. We have to remember that the CSH can be used in a lot of different contexts at the same time, so if this is going to be extra, super smart, I think we should name the history files with some context information along side the placement of where it has been invoked. But I'm not fully aware of how 🫣

This implementation does not set the location or name of the history file, this is entirely up to users (mainly CSH) to either:

• not use it ;)
• use it with their own file location, naming policy.

This change also does not change any current behaviour (apart from checking for NULL when adding to the history) so this change should be fairly safe.

[jeanbaptistelab]

These history files could also potentially end up containing sensitive information to some customers, so how do we protect that? If say, a command to VM is being entered with a password, then this would be forever locked into a history file. I'm not sure that is a problem or not, but it is something we need to consider.

A few things can be done:

• write a function that processes the line to be added to the history and guess whether some tokens look like password and replace them with "*"
• the user (CSH) can (temporarily) disable persisting the history for the next few commands and turn it back on again (the "history_file" pointer is part of the "struct slash", so saving it to a temp variable, setting it to NULL for the next few commands and restoring it is feasable. I'm contemplating extending the already existing built-in "history" command to add this functionality