CST_Subset: Correct subset indices for metadata

Hi @vagudets,

There is an issue in CST_Subset in this line.

library(CSTools)
load("/esarchive/scratch/erifarov/git/cstools/data/lonlat_temp_st.rda")
data <- CST_Subset(x = lonlat_temp_st$exp, along = c('ftime', 'sdate'), indices = list(2,5))

# Error in indices[[which(along == dim_along)]] : subscript out of bounds

# Corrected function
source("https://earth.bsc.es/gitlab/external/cstools/-/raw/develop-CST_Subset_metadata/R/CST_Subset.R")

If you agree I'll merge the branch since it's a small change.

Regards,
Eva