feat(datetime): add divider to datetime-action-buttons (#30509)

Issue number: internal

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## What is the new behavior?
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this PR. -->
Now, the action buttons have a divider for improved readability.

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

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1. Describe the impact and migration path for existing applications
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  2. Update the BREAKING.md file with the breaking change.
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See
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## Other information
[ionic
preview](https://ionic-framework-git-rou-11884-ionic1.vercel.app/src/components/datetime/test/basic?ionic:theme=ionic)
<!-- Any other information that is important to this PR such as
screenshots of how the component looks before and after the change. -->

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Co-authored-by: ionitron <[email protected]>

Author: JoaoFerreira-FrontEnd

core/src/components/datetime/datetime.ionic.scss

@@ -34,7 +34,7 @@
 
   margin-bottom: globals.$ion-space-200;
 
-  border-bottom: globals.$ion-border-style-solid globals.$ion-border-size-025 globals.$ion-primitives-neutral-300;
+  border-bottom: globals.$ion-border-style-solid globals.$ion-border-size-025 globals.$ion-primitives-neutral-400;
 }
 
 :host .datetime-header .datetime-title {
@@ -216,6 +216,17 @@
 
 // Calendar / Footer / Action Buttons
 // -----------------------------------
+:host .datetime-footer {
+  @include globals.padding(globals.$ion-space-200, 0, 0, 0);
+  @include globals.margin(globals.$ion-space-200, 0, 0, 0);
+  @include globals.border(
+    globals.$ion-border-style-solid globals.$ion-border-size-025 globals.$ion-primitives-neutral-400,
+    0,
+    0,
+    0
+  );
+}
+
 :host .datetime-buttons ion-buttons,
 .datetime-action-buttons .datetime-action-buttons-container {
   flex-flow: column;