Missing B2B module

[DrH97]

There seems to be no B2B implementation in the Package.

Detailed description

B2B and B2C are almost similar but there is only B2C implementation in the current version of the library (v2.1.1).

Context

This addition is important for those scenarios where one wants to have business to business transfers through mpesa.

Possible implementation

Similar to the BulkSender Class, a new class for B2B can be added with the changes specific to the new class.
The other changes are simple from there on.

Your environment

This is not really a bug but a feature addition.

• PHP 7.4, Laravel 6.16, mobile-money 2.1.1
• Ubuntu 18.04