Update the flow vis vignette with CRAN published version of mapgl add_flowmap

[e-kotov]

Pull Request

Description

This PR adds rendered interactive flowmap in the vignette 8 using the new mapgl version with official flowmap support (released to CRAN a few days ago).

Preview at: https://www.ekotov.pro/debiasR/articles/v08-visualising-flows.html#interactive-flow-map (I will delete the website to prevent accidental indexing by search engines). So it renders cleanly with existing pkgdown GitHub action.

Type of change

• Documentation update

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have added labels to the PR
• This change is proposed through a branch and PR, not a direct push to main
• I have run Rscript scripts/run_fast_tests.R or explained why it is not relevant
• If this touches Bayesian code, I have run the relevant optional Bayesian scope (rstanarm-smoke, latent-smoke, latent-stress, or all) or explained why it is not relevant
• Documentation or pkgdown-impacting changes have been checked with a local site build or CI

Related Issues

Follows up on #27, #63, #73.