Issue Proposal: Solutions to 3 MST questions

[Once-1296]

Minimum Spanning Tree (MST is one of the rather harder graph topics yet is quiet common as a learning outcome for most CS/IT professionals. LeetCode has 6 problems on MST,of which 3 are for all users. I propose to submit a solution using Kruskal's Algorithm. I already have solved these problems on own at my account Awwabcoder23 (https://leetcode.com/u/Awwabcoder23), and can quickly add the solutions under a subdirectory of C++ or DSA directory. Looking to a swift and easy merge.

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