Create VarInt writer

[pablitovicente]

Description

Create function varint(value: number, schema) => buffer

Motivation

lisk-codec will include a set of Writers for each data type defined in the LIP, to that end
we need a function to write VarInts.

Acceptance Criteria

• varint() should accept numbers (including bigInts)
• varint() returns a buffer that can be passed through the varInt reader to get the original value
• Code should be optimised for speed as much as possible
• Full test coverage
• Performance stats are provided based on the writing of values of different sizes and measure the writing of 100, 500, 1000, 30000 varints

Additional Information

Check if it will make sense to implement signed varints in same issue.

Related issues: #5200