[optimizer/rewriter] Create documentation for the optimizer and rewriter

[shubhambhokare1]

Create documentation for the optimizer and rewriter, feel free to add any cases we think we need to cover

### Tasks
- [ ] An example to show how to use the rewrite tool using the replacement by function name
- [ ] https://github.com/microsoft/onnxscript/issues/1361
- [ ] https://github.com/microsoft/onnxscript/issues/1049
- [ ] https://github.com/microsoft/onnxscript/pull/1413
- [ ] https://github.com/microsoft/onnxscript/pull/1482
- [ ] #1493

[gramalingam]

How about a section on the new IR?

[gramalingam]

All examples in documentation should also be actually run and validated (by the CI, etc.).

[justinchuby]

@shubhambhokare1 Would be nice to have a getting started page for the optimizer/rewriter to document the two-line code for running them