docs(extra.sql): add sql options docs (#3765)

## What is this PR for?

A small contribution to enhance the documentation and make it easier to
use.

While vim-dadbod and vim-dadbod-ui recommend using dotenv.vim for env
file injection, we aim to provide a simpler method. Instead of
implementing file parsing or relying on an external plugin (dotenv.vim),
just try directly using a Lua table.

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  why we should accept this pull request. -->

## Does this PR fix an existing issue?

none!

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  If this PR fixes any issues, please link to the issue here.
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## Checklist

- [x] I've read the
[CONTRIBUTING](https://github.com/LazyVim/LazyVim/blob/main/CONTRIBUTING.md)
guidelines.

lua/lazyvim/plugins/extras/lang/sql.lua

@@ -1,3 +1,31 @@
+if lazyvim_docs then
+  -- The setup below will automatically configure connections without the need for manual input each time.
+
+  -- Example configuration using dictionary with keys:
+  --    vim.g.dbs = {
+  --      dev = "Replace with your database connection URL.",
+  --      staging = "Replace with your database connection URL.",
+  --    }
+  -- or
+  -- Example configuration using a list of dictionaries:
+  --    vim.g.dbs = {
+  --      { name = "dev", url = "Replace with your database connection URL." },
+  --      { name = "staging", url = "Replace with your database connection URL." },
+  --    }
+
+  -- or
+  -- Create a `.lazy.lua` file in your project and set your connections like this:
+  -- ```lua
+  --    vim.g.dbs = {...}
+  --
+  --    return {}
+  -- ```
+
+  -- Alternatively, you can also use other methods to inject your environment variables.
+
+  -- Finally, please make sure to add `.lazy.lua` to your `.gitignore` file to protect your secrets.
+end
+
 local sql_ft = { "sql", "mysql", "plsql" }
 
 return {