Add fetchLDM() - access Kellogg Soil Survey Lab Data Mart via Soil Data Access or local SQLite snapshot

[brownag]

fetchLDM() development began in May 2021 when Soil Data Access began providing laboratory data. The method was later extended to work with a local data source such as an SQLite snapshot. It has been tested fairly extensively and is now ready to be made public.

• See this original PR which was accidentally merged and reverted: Fetch Lab Data Mart KSSL data with fetchLDM #182

#' Query data from Kellogg Soil Survey Laboratory Data Mart via Soil Data Access or local SQLite snapshot
#'
#' LDM model diagram: https://jneme910.github.io/Lab_Data_Mart_Documentation/Documents/SDA_KSSL_Data_model.html
#'
#' param x A vector of values to find in column specified by what, default NULL uses no constraints on what
#' param what A single column name from tables: lab_combine_nasis_ncss, lab_webmap, lab_site, lab_pedon or lab_area
#' param bycol A single column name from lab_layer used for processing chunks; default: "pedon_key"
#' param tables Avector of table names; Default is "lab_physical_properties", "lab_chemical_properties", "lab_calculations_including_estimates_and_default_values", and "lab_rosetta_Key". May also include one or more of: "lab_mir", "lab_mineralogy_glass_count", "lab_major_and_trace_elements_and_oxides", "lab_xray_and_thermal" but it will be necessary to select appropriate prep_code and analyzed_size_frac for your analysis (see Details).
#' param chunk.size Number of pedons per chunk (for queries that may exceed maxJsonLength)
#' param ntries Number of tries (times to halve chunk.size) before returning NULL; default 3
#' param layer_type Default: "horizon", "layer", and "reporting layer"
#' param prep_code Default: "S" and "". May also include one or more of: "F", "HM", "HM_SK" "GP", "M", "N", or "S"
#' param analyzed_size_frac Default: "<2 mm" and "". May also include one or more of: "<0.002 mm", "0.02-0.05 mm", "0.05-0.1 mm", "0.1-0.25 mm", "0.25-0.5 mm", "0.5-1 mm", "1-2 mm", "0.02-2 mm", "0.05-2 mm"
#' param dsn Data source name; either a path to a SQLite database, an open DBIConnection or (default) NULL (to use soilDB::SDA_query)
#'
#' details If the chunk.size parameter is set too large and the Soil Data Access request fails, the algorithm will re-try the query with a smaller (halved) chunk.size argument. This will be attempted up to 3 times before returning NULL
#'
#' Currently the lab_area tables are joined only for the "Soil Survey Area" related records.
#'
#' When requesting data from "lab_major_and_trace_elements_and_oxides", "lab_mineralogy_glass_count", or "lab_xray_and_thermal" multiple preparation codes (prep_code) or size fractions (analyzed_size_frac) are possible. The default behavior of fetchLDM() is to attempt to return a topologically valid (minimal overlaps) SoilProfileCollection. This is achieved by setting prep_code="S" ("sieved") and analyzed_size_frac="<2 mm". You may specify alternate or additional preparation codes or fractions as needed, but note that this may cause "duplication" of some layers where measurements were made with different preparation or on fractionated samples
#'
#' return a SoilProfileCollection for a successful query, a try-error if no site/pedon locations can be found or NULL for an empty lab_layer (within sites/pedons) result