Adding the feature of prelaoding weights a checkpoint.
This pull request **introduces 1 alert** and **fixes 1** when merging 7bc984d05a1cb0684428995fdc4135ef3b9a8c36 into 8f7c18973bf92f30679c0f4416412d629bfc7bff - [view on LGTM.com](https://lgtm.com/projects/g/NVIDIA/NeMo/rev/pr-0ebacc9e5c231176025a17986eb8897d98fa1097)

**new alerts:**

* 1 for Unnecessary delete statement in function

**fixed alerts:**

* 1 for Unused import This pull request **fixes 1 alert** when merging 3fba4784f3f42e6202037bcbdb7c7a06dc8a4a99 into 8f7c18973bf92f30679c0f4416412d629bfc7bff - [view on LGTM.com](https://lgtm.com/projects/g/NVIDIA/NeMo/rev/pr-983adf1d405bed3dd4227058e8a8c9047c3fbe26)

**fixed alerts:**

* 1 for Unused import This pull request **fixes 1 alert** when merging 92d986b0082037ea9361fae554bbac85242cfb9c into 8f7c18973bf92f30679c0f4416412d629bfc7bff - [view on LGTM.com](https://lgtm.com/projects/g/NVIDIA/NeMo/rev/pr-551286c4266b331d1384c6590727e7dd136d54eb)

**fixed alerts:**

* 1 for Unused import This pull request **fixes 1 alert** when merging 1b7abb9f53e57c7996beea694942c80c55e6f282 into 8f7c18973bf92f30679c0f4416412d629bfc7bff - [view on LGTM.com](https://lgtm.com/projects/g/NVIDIA/NeMo/rev/pr-7e37fc8f694b12466dd09daf59e11e66e4c7fc95)

**fixed alerts:**

* 1 for Unused import Can we get this merged? I'm not sure what we're trying to accomplish with this PR. As @titu1994 has said, we can already restore weights and finetune in NeMo with .nemo files. Or to resume training, we use PTL.

Can you please make it more clear in the README what feature is being added and how to use it?

Also, this PR is adding a new feature and should not be going into RC1. RC1 PRs are only for bug fixes and documentation.

Please rebase to main.
It enables user to start training by loading weights from another checkpoint ('.ckpt') or '.nemo' file. 

It can be done by setting the 'model.init_weights_from_model' parameter in the config or by:
model.load_weights_from_checkpoint(init_model_path='/path/to/model.nemo', strict=True)

It is a feature which enables fine-tuning out of the box for all nemo model/scripts/examples by just using the config.