DataFusion 18.0.0 Release

[andygrove]

Which issue does this PR close?

N/A

NOTE: I am testing out a new release process for this release, where I will create the rc tag directly on the branch-18 branch and release from there.

Advantages:

• The change log will match the release contents (no more race conditions during the release process)
• We keep this branch around indefinitely and can merge bug fixes here and release 18.x.x patch releases
• No risk of release activities slowing down any development on master branch

Rationale for this change

Regularly scheduled bi-weekly release

What changes are included in this PR?

• Update version
• Update changelog (rendered version)
• Update release process instructions

Are these changes tested?

Are there any user-facing changes?

[avantgardnerio]

Looks like normal release suff

[ursabot]

Benchmark runs are scheduled for baseline = 8a262c3 and contender = 0a5e8ae. 0a5e8ae 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