MINOR: Optimizer example and docs, deprecate Expr::name

[andygrove]

Which issue does this PR close?

N/A

Rationale for this change

I want to make it easier for new contributors to be able to write and review optimization rules.

You can see the rendered version of the new README here

What changes are included in this PR?

• Example
• Docs
• Rename Expr::name() to Expr::display_name()
• Add deprecated Expr::name() that delegates to Expr::display_name()

Are there any user-facing changes?

No

[isidentical]

Does it make sense to emphasize that in the event of there are no transformations to apply (for the given input), the optimizer could (and should) return the input as is (e.g. instead of failing with an exception)?

/// `OptimizerRule` can transform one ['LogicalPlan'] into another which
/// computes the same results, but in a potentially more efficient way. If
/// there are no suitable transformations for the input plan, the optimizer can
/// simply return it as is.

[andygrove]

That's a very good point. I will add this.

[alamb]

very nice @andygrove 👌

[alamb]

I personally recommend putting this example into datafusion/examples rather than datafusion/optimizer/examples so that it is easier to find

[andygrove]

Done

[ursabot]

Benchmark runs are scheduled for baseline = a226587 and contender = 4cb8ac0. 4cb8ac0 is a master commit associated with this PR. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on ec2-t3-xlarge-us-east-2] ec2-t3-xlarge-us-east-2
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on test-mac-arm] test-mac-arm
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on ursa-i9-9960x] ursa-i9-9960x
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on ursa-thinkcentre-m75q] ursa-thinkcentre-m75q
Buildkite builds:
Supported benchmarks:
ec2-t3-xlarge-us-east-2: Supported benchmark langs: Python, R. Runs only benchmarks with cloud = True
test-mac-arm: Supported benchmark langs: C++, Python, R
ursa-i9-9960x: Supported benchmark langs: Python, R, JavaScript
ursa-thinkcentre-m75q: Supported benchmark langs: C++, Java

[alamb]

🎉