Add support for choosing k layers for injection

[nniranjhana]

Presently both the static and dynamic injections in the layer states and layer outputs respectively are an all or one feature i.e. either all the layers can be chosen for injection (Mode: multiple in YAML file) or one layer can be randomly chosen for injection (Mode: single in YAML file).

Add support for user to specify what k layers to inject (where k = {k₁, k₂, k₃, .. k_n} and every k_i is an integer between [1, n] where n is the total number of layers in the model).

1. For static or layer states injection, it is straight forward to do.
2. For dynamic or layer outputs injection, it might be better to address the issue Generalize injection in layer outputs for non-linear architectures #2 first before tackling this since the code is dependent on the way we splice layers during injection and the methodology could change while fixing Generalize injection in layer outputs for non-linear architectures #2.