Change get_sotkanet default years, add function sotkanet_indicators_metadata and move from httr to httr2

[Allaht2]

Change get_sotkanet years parameter default from 1991:2015 to NULL. The default now gives the data from all the available years. Also update the function documentation and add more examples.
Add function sotkanet_indicators_metadata and update other functions to use it instead of SotkanetIndicatorsMetadata.

[Allaht2]

Move from httr to httr2. All the old and new functions that used httr functions now use httr2 functions instead.

[pitkant]

Good work

[pitkant]

Here flatten = TRUE but in sotkanet.json_query function the parameters is not passed forward anymore (?)

[pitkant]

Is the output still the same as before? Is simplifyVector essentially the same as flatten = TRUE?

[Allaht2]

My understanding is that simplifyVector does work in a similar way. At least in my testing the output is similar with simplifyVector.

[pitkant]

Maybe remove eurostat reference and instruct user to just try with other options

[pitkant]

Maybe one final addition: since packages like kableExtra and ggplot2 are only in Suggests and not Depends, their presence/absence could be used to control the evaluation of vignette building? Like this:

eval = requireNamespace("somedependency")
eval = !identical(Sys.getenv("SOME_THING_YOU_NEED"), "")
eval = file.exists("credentials-you-need")

See Vignettes - Special considerations for vignette code for more info.