GP-146 - new Heterogeneous Max Holder Exercise

* add HeterogeneousMaxHolder with javadocs
* add HeterogeneousMaxHolderTest.java that provides test
* add README.MD
* update pom.xml

Author: tboychuk

1-0-java-basics/1-3-2-heterogeneous-max-holder/README.MD

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+# <img src="https://raw.githubusercontent.com/bobocode-projects/resources/master/image/logo_transparent_background.png" height=50/>Heterogeneous Max Holder
+#### Improve your generics-related skills implementing a multi-type max holder container 💪
+
+### Objectives
+* create a container class that uses *a type token* ✅
+* declare a generic type parameter that is `Comparable` ✅
+* implement a generic method put that stores max values by its type ✅
+* overload a generic method put with a custom `Comparator` ✅
+* implement a generic method getMax that retrieves a max value by its type ✅
+* wrap a comparator instance to make it null-safe ✅
+
+---
+#### 🆕 First time here? – [See Introduction](https://github.com/bobocode-projects/java-fundamentals-exercises/tree/main/0-0-intro#introduction)
+#### ➡️ Have any feedback? – [Please fill the form ](https://forms.gle/u6kHcecFuzxV232LA)
+
+##
+<div align="center"><img src="https://raw.githubusercontent.com/bobocode-projects/resources/master/animation/GitHub%20Star_3.gif" height=50/></div>

1-0-java-basics/1-3-2-heterogeneous-max-holder/pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <parent>
+        <artifactId>1-0-java-basics</artifactId>
+        <groupId>com.bobocode</groupId>
+        <version>1.0-SNAPSHOT</version>
+    </parent>
+    <modelVersion>4.0.0</modelVersion>
+
+    <artifactId>1-3-2-heterogeneous-max-holder</artifactId>
+    
+</project>

1-0-java-basics/1-3-2-heterogeneous-max-holder/src/main/java/com/bobocode/basics/HeterogeneousMaxHolder.java

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+package com.bobocode.basics;
+
+import java.util.Map;
+
+/**
+ * {@link HeterogeneousMaxHolder} is a multi-type container that holds maximum values per each type. It's kind of a
+ * key/value map, where the key is a type and the value is the maximum among all values of this type that were put.
+ * <p>
+ * It's based on the {@link Map} and provides an API that allows to put a value by type, and get a max value by type.
+ */
+public class HeterogeneousMaxHolder {
+
+    /**
+     * A method put stores a provided value by its type, if the value is greater than the current maximum. In other words, the logic
+     * of this method makes sure that only max value is stored and everything else is ignored.
+     * <p>
+     * If the current max value is less than a provided one, or if it's null, then a provided value gets stored and the old
+     * max is returned. Otherwise, nothing new is added, and the provided value is returned.
+     * <p>
+     * So technically, this method always stored the greater value and returns the smaller one.
+     *
+     * @param key   a provided value type
+     * @param value a value to put
+     * @param <T>   value type parameter
+     * @return a smaller value among the provided value and the current maximum
+     */
+    // todo: implement a method according to javadoc
+
+    /**
+     * An overloaded method put implements the same logic using a custom comparator. A given comparator is wrapped with 
+     * a null-safe comparator, considering null smaller than any non-null object. 
+     *
+     * All arguments must not be null.
+     *
+     * @param key        a provided value type
+     * @param value      a value to put
+     * @param comparator a custom comparator for the given type
+     * @param <T>        value type parameter
+     * @return a smaller value among the provided value and the current maximum
+     */
+    // todo: implement a method according to javadoc
+
+    /**
+     * A method getMax returns a max value by the given type. If no value is stored by this type, then it returns null.
+     *
+     * @param key a provided value type
+     * @param <T> value type parameter
+     * @return current max value or null
+     */
+    // todo: implement a method according to javadoc
+}