fix(docs): update example result, when using null_override = false (#33)

This pull request updates documentation examples to accurately reflect
the behavior of the `deep_merge` function when merging values with
`null` and `null_override = false`.

Documentation corrections:

* Updated the example result in `docs/functions/deep_merge.md` to show
that `optional_setting` retains its original value ("enabled") when
overridden with `null` and `null_override = false`.
* Made the same correction in `internal/provider/deep_merge_function.md`
for consistency and accuracy.
* Changes have been also tested

```
> provider::lara-utils::deep_merge([{ name = "service", port = 8080, optional_setting = "enabled" }, { port = 9090, optional_setting = null }], { null_override = true })
{
  "name" = "service"
  "optional_setting" = null
  "port" = 9090
}
> provider::lara-utils::deep_merge([{ name = "service", port = 8080, optional_setting = "enabled" }, { port = 9090, optional_setting = null }], { null_override = false })
{
  "name" = "service"
  "optional_setting" = "enabled"
  "port" = 9090
}
```

Author: Riqardos

docs/functions/deep_merge.md

@@ -61,7 +61,7 @@ locals {
   overrides = { port = 9090, optional_setting = null }
 
   result = provider::lara-utils::deep_merge([local.base, local.overrides], { null_override = false })
-  # Result: { name = "service", port = 9090, optional_setting = null }
+  # Result: { name = "service", port = 9090, optional_setting = "enabled" }
   # Note: null doesn't override the existing value
 }
 ```

internal/provider/deep_merge_function.md

@@ -51,7 +51,7 @@ locals {
   overrides = { port = 9090, optional_setting = null }
 
   result = provider::lara-utils::deep_merge([local.base, local.overrides], { null_override = false })
-  # Result: { name = "service", port = 9090, optional_setting = null }
+  # Result: { name = "service", port = 9090, optional_setting = "enabled" }
   # Note: null doesn't override the existing value
 }
 ```