Addition and improvevent of Description field for all metrics of index data size metrics pages

The difference between the data_size and raw_data_size is quite important, and is an issue we see come up frequently in support cases.

A lot of customers assume these stats mean compressed and uncompressed. This is not true. Both refer to an uncompressed index size across both memory and disk.

data_size refers to the size of items in an index and the size of the operations in its delta list. This means if user deletes/updates documents, this stat can still go up even if there are no new items in the index.

raw_data_size is just the size of the items in the index.

Please refer to this slack thread from the indexing team which explains it a bit more thoroughly.