[feature-1] Trapping Rain Water added in CPP

[kiruba-r11]

Related Issues

• Added an important problem named Trapping Rain Water.

Closes: #254

Describe the changes you've made

I have completely implemented a CPP program that takes the input of array elements from the user and prints the amount of rainwater that can be trapped.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, local variables)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

This has been tested by generating a set of random inputs using a generator and verified the outputs manually.

Describe if there is any unusual behavior of your code(Write NA if there isn't)

NA

Checklist:

• My code follows the style guidelines of this project.
• I have performed a self-review of my own code.
• I have commented on my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.

[kiruba-r11]

@ankitapuri Please have a look at it