Expense Backend

[vignesh-6145]

This Issue keeps track of all the backend development progressed

Requirements

• [x] #17
• [x] #23
• [x] Add a REST to Retrieve the required Expenses or all the Expenses
• [x] #19
• [x] #21

[vignesh-6145]

The requirements were fulfilled , for future changes there will be a new parent Issue raised in near feature

thanks @bandla88 for helping and guiding me in accomplishing tasks