Adds interruption support for v0.2.8

[johnedquinn]

Relevant Issues

• See the same addition to main (for v0.13.1's release): Adds support for thread interruption in compilation and execution #1211

Description

• The base of this PR is branch v0_2_8_SNAPSHOT which is at the tag v0.2.7-alpha.
• I will be releasing this as v0.2.8. Please see each commit.
• Also, I needed to remove the publish workflow, or else the GH pages would've been overridden. And, I needed to update the pull_request workflow to use ubuntu-latest since 18.04 is now unsupported, see this SO post.

Release Notes

As there isn't a CHANGELOG at this state of our codebase, here is what will be released:

Release v0.2.8

This release adds support for thread interruption of the CompilerPipeline during compilation and evaluation of long-running queries. To consume this capability, you must opt-in by setting interruptible to true in the CompileOptions. The changes ensure that evaluation of long-running scans and joins can be interrupted as well as the compilation of long-running aggregations.

• Note: the interruption of compilation of aggregations was specifically catered for as there is a bug in the compilation of aggregations that causes premature materialization of the data. Therefore, if you intend on interrupting your queries, it may also be a good idea to interrupt at the compilation phase. You may still interrupt at evaluation.
• Note: This addition is NOT added in later versions. If you plan on migrating to a later version, these changes are only present in v0.13.1+. To upgrade, please see the CHANGELOG of v0.13.1 which talks about the addition of thread interruption.

Other Information

• Updated Unreleased Section in CHANGELOG: NO -- there is no changelog
• Any backward-incompatible changes? NO
• Any new external dependencies? NO
• Do your changes comply with the Contributing Guidelines
  and Code Style Guidelines? YES

License Information

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[alancai98]

As a followup, could also update the CHANGELOG in main to include the v0.2.8 entry.