examples: add RNN examples

[shu1chen]

Description

Add examples for Vanilla RNN and Linear-before-reset GRU RNN by referring to the RNN descriptions in oneDNN documentation.
For lbr_gru, the gates order is update, reset and output gate, and there is an extra bias for u' gate.

Checklist

General

• Do all unit and benchdnn tests (make test and make test_benchdnn_*) pass locally for each commit?
• Have you formatted the code using clang-format?

[mgouicem]

Thank you very much for the PR.
Could you please change the commit names to align with oneDNN contribution guidelines?
Something like:
examples: add vanilla_rnn example
examples: add lbr_gru example

Could you also please add reference to those examples in the documentation? (at the end of file doc/primitives/rnn.md)

Thanks you!

[shu1chen]

Thanks for reviewing. I have updated the commit messages and also added reference to those examples in the documentation.

[mgouicem]

Thanks for the PR!