ARROW-16252: [CI][Archery] Highlight number of failed builds on nightly reports

[raulcd]

This PR adds to the reports email subject the number of tasks that are pending and have failied.
Tested locally with a reduced number of tasks:

$ archery crossbow report --no-fetch nightly-packaging-2022-04-14-0
From: None <None>
To: None
Subject: [NIGHTLY] Arrow Build Report for Job nightly-packaging-2022-04-14-0: 2 failed, 0 pending


Arrow Build Report for Job nightly-packaging-2022-04-14-0

All tasks: https://github.com/raulcd/crossbow/branches/all?query=nightly-packaging-2022-04-14-0

Errored Tasks:
- debian-bookworm-arm64:
  URL: https://github.com/raulcd/crossbow/tree/nightly-packaging-2022-04-14-0-travis-debian-bookworm-arm64
- wheel-windows-cp310-amd64:
  URL: https://github.com/raulcd/crossbow/tree/nightly-packaging-2022-04-14-0-github-wheel-windows-cp310-amd64

[github-actions]

https://issues.apache.org/jira/browse/ARROW-16252

[kszucs]

Thanks @raulcd !

[ursabot]

Benchmark runs are scheduled for baseline = b8be05b and contender = c38a32e. c38a32e is a master commit associated with this PR. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Finished ⬇️0.0% ⬆️0.0%] ec2-t3-xlarge-us-east-2
[Finished ⬇️0.67% ⬆️0.17%] test-mac-arm
[Failed ⬇️0.38% ⬆️0.0%] ursa-i9-9960x
[Finished ⬇️0.43% ⬆️0.09%] ursa-thinkcentre-m75q
Buildkite builds:
[Finished] <https://buildkite.com/apache-arrow/arrow-bci-benchmark-on-ec2-t3-xlarge-us-east-2/builds/552| c38a32ef ec2-t3-xlarge-us-east-2>
[Finished] <https://buildkite.com/apache-arrow/arrow-bci-benchmark-on-test-mac-arm/builds/540| c38a32ef test-mac-arm>
[Failed] <https://buildkite.com/apache-arrow/arrow-bci-benchmark-on-ursa-i9-9960x/builds/538| c38a32ef ursa-i9-9960x>
[Finished] <https://buildkite.com/apache-arrow/arrow-bci-benchmark-on-ursa-thinkcentre-m75q/builds/550| c38a32ef ursa-thinkcentre-m75q>
[Finished] <https://buildkite.com/apache-arrow/arrow-bci-benchmark-on-ec2-t3-xlarge-us-east-2/builds/551| b8be05b7 ec2-t3-xlarge-us-east-2>
[Finished] <https://buildkite.com/apache-arrow/arrow-bci-benchmark-on-test-mac-arm/builds/539| b8be05b7 test-mac-arm>
[Failed] <https://buildkite.com/apache-arrow/arrow-bci-benchmark-on-ursa-i9-9960x/builds/537| b8be05b7 ursa-i9-9960x>
[Finished] <https://buildkite.com/apache-arrow/arrow-bci-benchmark-on-ursa-thinkcentre-m75q/builds/549| b8be05b7 ursa-thinkcentre-m75q>
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