Added boring model as a ipynb so it can be updated

[jiwidi]

What does this PR do?

Fixes #10490

This PR adds the boring model notebook along with a needed fix on an outdated import. The purpose of this PR is so the google colab linking to the boring model aims at the ipynb version on master, allowing the PL team to update and mantain the notebook within github.

If this PR moves forward, the default issue link should be updated.

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[rohitgr7]

1. Shall we remove the torchmetrics from the bug report model? The reason to remove torchmetrics is we don't want user to explicitly install it always since its a completely separate package and also accuracy imported isn't used anywhere.
2. Shall we remove bolts requirements? Whatever's imported from bolts isn't used either.
3. Keep both notebook and script under pl_examples/bug_report/<.py and .ipynb>??

[tchaton]

• Shall we remove the torchmetrics from the bug report model? The reason to remove torchmetrics is we don't want user to explicitly install it always since its a completely separate package and also accuracy imported isn't used anywhere.
• Shall we remove bolts requirements? Whatever's imported from bolts isn't used either.
• Keep both notebook and script under pl_examples/bug_report/<.py and .ipynb>??

We should also drop torch vision, Mnist import. Let's keep it minimal.

[jiwidi]

I'll change the imports again and add the colab link to the github issue template then!

[carmocca]

LGTM

For any reviewers, you can check the Notebook with this link:
https://colab.research.google.com/github/jiwidi/pytorch-lightning/blob/master/pl_examples/bug_report/The_BoringModel.ipynb

[tchaton]

LGTM ! Much cleaner !