JDTLS example is not quite right

### Checklist

- [X] I have searched through the AstroNvim docs
- [X] I have searched through the existing issues of AstroNvim
- [X] I have searched the existing issues of plugins related to this issue

### Neovim version (nvim -v)

0.9.4

### Operating system/version

NixOs 23

### Terminal/GUI

Alacritty

### Describe the bug

In the example given in https://docs.astronvim.com/recipes/advanced_lsp/#java-nvim-jdtls a new folder is created every time neovim is executed. And it concatenates the cwd so a new folder will be created by the name of the cwd even if it's not a java project.

```
local project_name = vim.fn.fnamemodify(vim.fn.getcwd(), ":p:h:t")
local workspace_dir = vim.fn.stdpath "data" .. "/site/java/workspace-root/" .. project_name

os.execute("mkdir " .. workspace_dir)
```


Additionally, `os.execute` does not work when the shell is `nushell`. Error of that actually visible for 200ms. I had to record and go frame by frame to read the error message. `vim.fn.mkdir()` probably a good alternative.


### Steps to Reproduce

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### Expected behavior

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### Screenshots

_No response_

### Additional Context

_No response_