Automate generation of release PRs

[iajoiner]

Which issue does this PR close?

Closes #2735 .

Rationale for this change

Automates the production of bimonthly release PRs.

What changes are included in this PR?

• dev/release/file_release_pr.sh which automates filing of the release PRs.
• Changes in dev/release/README.md to accommodate this PR as well as Automate updates to CHANGELOG-old.md #2732 .

Are there any user-facing changes?

No.

[iajoiner]

@andygrove @alamb I think once our individual scripts are done the entire release process probably needs to be automated haha.

[alamb]

I am going to try this for this next release -- thanks @iajoiner

[ursabot]

Benchmark runs are scheduled for baseline = 76da624 and contender = 35c313b. 35c313b 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-rs-commits is not supported on ec2-t3-xlarge-us-east-2] ec2-t3-xlarge-us-east-2
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on test-mac-arm] test-mac-arm
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on ursa-i9-9960x] ursa-i9-9960x
[Skipped ⚠️ Benchmarking of arrow-rs-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