Add attribute to repos, to increase harmony for renv users

[juliasilge]

Related to:

• Opt users into using PPM when using default repos on Positron rstudio/renv#1963
• `renv::install("duckdb")` hangs indefinitely #4214

In Positron, we do in fact set repos to "https://cran.rstudio.com/" the same as RStudio:

https://github.com/posit-dev/ark/blob/9387883055176bb0493b9893cd392f53a1bda0ed/crates/ark/src/modules/positron/options.R#L30-L45

But RStudio also adds an attribute:

getOption("repos")
#>                        CRAN 
#> "https://cran.rstudio.com/" 
#> attr(,"RStudio")
#> [1] TRUE

^{Created on 2024-08-06 with reprex v2.1.1}

Let's add an attribute of "Positron" so that renv can pick it up in its logic for deciding whether to use PPM.

[juliasilge]

Once we bump ark, we can verify that we now see an attribute on this option:

getOption("repos")
#>                        CRAN 
#> "https://cran.rstudio.com/" 
#> attr(,"IDE")
#> [1] TRUE

^{Created on 2024-09-04 with reprex v2.1.1}

I will also need to update at rstudio/renv#1963 once this is in a publicly available release build.

[testlabauto]

Verified Fixed

Positron Version(s) : 2024.09.0-11
OS Version          : OSX

Test scenario(s)

getOption("repos")

CRAN
"https://cloud.r-project.org"

Link(s) to TestRail test cases run or created:
N/A