Use the same plotlyjs version number for all imports

[fonsp]

This PR makes sure that the same version of the plotlyjs web asset is used for all imports: through artifact or through CDN.

This also adds _js_version and _js_path as public API: this means other packages can depend on PlotlyJS.jl to get the plotly.min.js asset. Used in https://github.com/JuliaPlots/Plots.jl/pull/4862

[codecov-commenter]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (43d38e9) 37.50% compared to head (b2532bc) 36.51%. Report is 5 commits behind head on master.

Files	Patch %	Lines
src/PlotlyJS.jl	50.00%	3 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #480 +/- ## ========================================== - Coverage 37.50% 36.51% -0.99% ========================================== Files 4 4 Lines 288 293 +5 ========================================== - Hits 108 107 -1 - Misses 180 186 +6 ``` | [Flag](https://app.codecov.io/gh/JuliaPlots/PlotlyJS.jl/pull/480/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaPlots) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/JuliaPlots/PlotlyJS.jl/pull/480/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaPlots) | `36.51% <50.00%> (-0.99%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaPlots#carryforward-flags-in-the-pull-request-comment) to find out more.

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[fonsp]

Thanks! Could you also make a release? Then we can work on https://github.com/JuliaPlots/Plots.jl/pull/4862

[fonsp]

Thanks again :)