Introductory tutorial on mid-circuit measurements (#1094)

**Title:**
Introduction to mid-circuit measurements

**Summary:**
In this tutorial, we will dive into the basics of mid-circuit
measurements with PennyLane. Readers will learn about
- basic measurement processes in quantum mechanics,
- the impact of a measurement on one- and two-qubit systems,
- postselection and qubit reset, and
- dynamic quantum circuits powered by conditional operations.

**Relevant references:**
See demo references and related content, in particular
`tutorial_how_to_collect_mcm_stats` and
`tutorial_how_to_create_dynamic_mcm_circuits`.

**Possible Drawbacks:**

**Related GitHub Issues:**

----
If you are writing a demonstration, please answer these questions to
facilitate the marketing process.

* GOALS — Why are we working on this now?
This tutorial promotes mid-circuit measurement functionality in
PennyLane, which has been extended in recent releases.
In addition, this tutorial is part of the broader goal of emphasizing
MCMs and dynamic circuits in our contents.

* AUDIENCE — Who is this for?
Beginners in PennyLane coding that want to learn about mid-circuit
measurements

* KEYWORDS — What words should be included in the marketing post?
  - Mid-circuit measurements
  - Measurements in quantum mechanics
  - Dynamic circuits

* Which of the following types of documentation is most similar to your
file?
(more details
[here](https://www.notion.so/xanaduai/Different-kinds-of-documentation-69200645fe59442991c71f9e7d8a77f8))
    
- [x] Tutorial
- [ ] Demo
- [ ] How-to

---------

Co-authored-by: Guillermo Alonso-Linaje <[email protected]>
Co-authored-by: Thomas R. Bromley <[email protected]>
Co-authored-by: Korbinian Kottmann <[email protected]>
Co-authored-by: Josh Izaac <[email protected]>
Co-authored-by: Ivana Kurečić <[email protected]>

demonstrations/tutorial_mcm_introduction.metadata.json

@@ -0,0 +1,53 @@
+{
+    "title": "Introduction to mid-circuit measurements",
+    "authors": [
+        {
+            "id": "david_wierichs"
+        }
+    ],
+    "dateOfPublication": "2024-05-10T00:00:00+00:00",
+    "dateOfLastModification": "2024-05-10T00:00:00+00:00",
+    "categories": [
+        "Getting Started",
+        "Quantum Computing"
+    ],
+    "tags": [],
+    "previewImages": [
+        {
+            "type": "thumbnail",
+            "uri": "/_static/demonstration_assets/regular_demo_thumbnails/thumbnail_mcm_introduction.png"
+        },
+        {
+            "type": "large_thumbnail",
+            "uri": "/_static/large_demo_thumbnails/thumbnail_large_mcm_introduction.png"
+        }
+    ],
+    "seoDescription": "Learn the basics of mid-circuit measurements and how to use them in PennyLane.",
+    "doi": "",
+    "canonicalURL": "/qml/demos/tutorial_mcm_introduction",
+    "references": [],
+    "basedOnPapers": [],
+    "referencedByPapers": [],
+    "relatedContent": [
+        {
+            "type": "demonstration",
+            "id": "tutorial_how_to_create_dynamic_mcm_circuits",
+            "weight": 1.0
+        },
+        {
+            "type": "demonstration",
+            "id": "tutorial_how_to_collect_mcm_stats",
+            "weight": 1.0
+        },
+        {
+            "type": "demonstration",
+            "id": "tutorial_mbqc",
+            "weight": 1.0
+        },
+        {
+            "type": "demonstration",
+            "id": "tutorial_teleportation",
+            "weight": 1.0
+        }
+    ]
+}