Fix install + dashboard rendering with bundled demo data

[amcim]

Description

This PR's focus is to allow the shiny app to work on the included external data, and thus user, input, when before it was defaulting to ESKAPE pathogens. This led to the dashboards being broken and not usable

• Moved countrycode to Imports from Suggests. This was done because it was very noticable just having a major panel giving an error and would confuse a user
• Guarded ComplexHeatmap::draw(ht...) calls with req to deal with no data render on empty panels
• Removed observer on the Bug/Drug feature comparison tab that attempted to hardcode ESKAPE labels
• Fixed a crash involving the legend in makeCrossModelPerformancePlot() which appears when there is only one unique strat value
• Populated the Model holdouts Bug/Drug selectors to the loaded data. They were previously empty so the tab was not usable

What kind of change(s) are included?

• Feature (adds or updates new capabilities)
• Bug fix (fixes an issue).
• Enhancement (adds functionality).
• Breaking change (these changes would cause existing functionality to not work as expected).

Checklist

Please ensure that all boxes are checked before indicating that this pull request is ready for review.

• I have read and followed the CONTRIBUTING.md guidelines.
• I have searched for existing content to ensure this is not a duplicate.
• I have performed a self-review of these additions (including spelling, grammar, and related).
• I have added comments to my code to help provide understanding.
• I have added a test which covers the code changes found within this PR.
• I have deleted all non-relevant text in this pull request template.
• Reviewer assignment: Tag a relevant team member to review and approve the changes.

[eboyer221]

Some issues are fixed by previous PRs that have not yet been merged. (e.g. the conversion to plotly fixes crash in makeCrossModelPerformancePlot legend with single strat value, Populate Model holdouts Bug/Drug selectors).

With regard to amRviz/amRshiny specifically if folks could review & approve in this order:

#18— install + dashboard rendering fix from @Alex McKim
#20— package rename from amRshiny to amRviz + new visualizations

After #20 merges I will need to rebase #16 onto the new main and update any 'amrShiny' -> 'amRviz' references in the test files and then #16 could be reviewed after that process is completed.
3. #16— unit tests (review after #20 merges; will need rebase to pick up the package rename)

If those PRs are merged I can likely just close #14  without merging and open up small follow-up PRs for the minor UI changes (color palette, home page redesign, etc.) that introduced.

[eboyer221]

Approving, I pulled the branch and ran locally. Confirmed the Model Holdouts Bug dropdown now populates, and the country choropleth renders correctly.