adding file.temp_file to eldritch

[adm1nPanda]

What type of PR is this?

/feature
/kind eldritch-function

What this PR does / why we need it:

Implemented file.temp_file()

Which issue(s) this PR fixes:

Fixes #788

[hulto]

Oops sorry @adm1nPanda i should have been more clear in the issue description.
For this feature we'd like to leverage the OSes default tmp system.
/tmp/ on linux, /var/private/tmp/*/*/* on mac, C:\Users\AppData\Local\Temp (i think) on Windows. You shouldn't need to specify the tmp dir path the library should handle that for you.

To do this we can leverage the temp file library we've been using and it looks like the .keep() call you're making is exactly what we need.

Instead of a random file name in a specified dir i'd like to create a tmp file in and optionally specify the name of that file.

The file should be empty and the function should return the path to the newly created file.

[hulto]

Awesome! Just a couple changes then should be good 🤌

[hulto]

Clarified how to do optional parameters.

This way lets users do something like:

tmp_file = file.temp()
# - or -
name_tmp_file = file.temp("special_name.txt")

[hulto]

Couple nits that you can ignore if you want.
One small change please.

[hulto]

Nice!
Some optional nits if you want but this looks good to me! 🙂