PR: Fix tour images shared between versions properly w/unique paths

[CAM-Gerlach]

Pull Request

Pull Request Checklist

• [x] Read and followed this repo's Contributing Guidelines
• [x] Based your PR on the latest version of the correct branch (master or 4.x)
• [x] Checked your writing carefully for correct English spelling, grammar, etc
• [x] Described your changes and the motivation for them below
• [x] Noted what issue(s) this pull request resolves, creating one if needed

Description of Changes

Unfortunately, after testing, PR #287 did not fix the issue, as sphinx-multiversion inexplicably copied even extra-specified dirs copied from the base build branch, not the current branch. In order to work around this, the least hacky approach appears to be to just write version-unique assets to version-unique paths, and hardcode the version in the path to the asset on each branch. The same strategy can be used if and when we want to use unique steps/step descriptions, coupled with storing these data in a JSON files in a versioned subdir of assets, coupled with making a call to the quickstart trigger code including the versioned data path to load into an inline <script> block inside the raw directive in the quickstart source files, so it loads the version-specific data (will take a bit of work, so defering for now until it is needed).

Issue(s) Resolved

Fixes #268 (properly)

[CAM-Gerlach]

Merging, because there's no proper way to fully test without doing so and I'll need to do a custom merge to master.