Improve startup error handling and reporting for plugins

[har7an]

Moved from #1753:

I'd like to call out an example of how error handling could be improved that is easily reproduced.

I recently messed with my filesystem with specific goals in mind and a side effect that I missed was my user's .cache directory getting owned by root. Everything I previously used could still function since those .cache artifacts already existed and were still owned by me. zellij was the first new thing I tried since this mistake.

When starting zellij for the first time it crashed with a pretty verbose file not found and permission denied error but no specifics as to the file. I then tried the recommended RUST env var to get more info, but the backtrace was unusable as it was all <unknown> entries.

The only reason I found /tmp/zellij-1000/zellig-log was because I also tried strace against zellij. That log is the only place I got usable info to solve my problem as it specifically stated failed to create datadir in ".../.cache/...". So the quick and easy improvement is to mention the log file in the error messages. The other improvement would be getting the same information that's in the log file into the error message that's displayed to the user.

Originally posted by @alaricljs in #1753 (comment)

[har7an]

@alaricljs I'm moving your comment over here so we can discuss your suggestions better.

First: Thanks for raising this issue!

I had a look at the code and you're totally right. The error is being recognized, but the wrong error is reported to the user. I've already changed that in my development version so the situation will now be much clearer to begin with.

About the logfile: I have rewritten the panic message to include this bit of information, it now looks like this:

  × Thread 'wasm' panicked.
  ├─▶ Originating Thread(s)
  │   	1. ipc_server: NewClient
  │   	2. screen_thread: NewTab
  │   	3. plugin_thread: NewTab
  │   
  ├─▶ At zellij-server/src/lib.rs:745:18
  ╰─▶ Program terminates: a fatal error occured
      
      Caused by:
          0: failed to load plugin for client 1
          1: failed to start plugin PluginConfig {
               [ ... ]
          2: failed to create datadir in "/var/home/hartan/.cache/zellij/zellij:tab-bar"
          3: Permission denied (os error 13)
  help: If you are seeing this message, it means that something went wrong.
        
        -> To get additional information, check the log at: /tmp/zellij-1000/zellij-log/zellij.log
        -> To see a backtrace next time, reproduce the error with: RUST_BACKTRACE=1 zellij [...]
        -> To help us fix this, please open an issue: https://github.com/zellij-org/zellij/issues

Do you think this is an improvement over the previous situation? Would you like to see something else as part of the panic message, any additional information we may give to users?

About the backtrace: We are aware of this problem and looking for a way to fix it.

[alaricljs]

Hey @har7an, looks good and I can't think of anything else that would have been helpful.