add table -> table to into datetime (#9775)

should close https://github.com/nushell/nushell/issues/9774

# Description
given the help page of `into datetime`, 
```
Parameters:
  ...rest <cellpath>: for a data structure input, convert data at the given cell paths
```
it looks like `into datetime` should accept tables as input 🤔 

this PR
- adds the `table -> table` signature to `into datetime`
- adds a test to make sure the behaviour stays there

crates/nu-command/src/conversions/into/datetime.rs

@@ -68,7 +68,9 @@ impl Command for SubCommand {
             (Type::Int, Type::Date),
             (Type::String, Type::Date),
             (Type::List(Box::new(Type::String)), Type::List(Box::new(Type::Date))),
+            (Type::Table(vec![]), Type::Table(vec![])),
         ])
+        .allow_variants_without_examples(true)
         .named(
                 "timezone",
                 SyntaxShape::String,

crates/nu-command/tests/commands/into_datetime.rs

@@ -0,0 +1,8 @@
+use nu_test_support::nu;
+
+#[test]
+fn into_datetime_table_column() {
+    let actual = nu!(r#"[[date]; ["2022-01-01"] ["2023-01-01"]] | into datetime date"#);
+
+    assert!(actual.out.contains(" ago"));
+}

crates/nu-command/tests/commands/mod.rs

@@ -39,6 +39,7 @@ mod help;
 mod histogram;
 mod insert;
 mod inspect;
+mod into_datetime;
 mod into_filesize;
 mod into_int;
 mod join;