Flexible time zone handling

[bpbond]

This PR adds time zone conversion capabilities to L1_normalize.qmd. In other words, we now can process data from sites with catalogers set to different local times, and everything is converted to a single output timezone (by default, "Etc/GMT+5" or EST) in the output.

A small data file from a fake site "TZTEST" in a different time zone is included in the ./data_TEST/Raw/ to exercise the timestamp-adjustment code in L1_normalize.

Raw file:

After L1_normalize processing:

You can see that the TZTEST site's data (in central standard time, per the L1_metadata_timezones.csv file) is now in Eastern time.

The output time zone information is now written to both the overall README

COMPASS-FME Level 1 data
Version: ???
Date: ???
Observations: 40,890
Data time zone: Etc/GMT+5
Git commit: e55d476

and site-specific metadata files:

File columns:
—----------------------------------
Site            Site code; see site info above (character)
Plot            Plot code; see site info above (character)
TIMESTAMP       Datalogger timestamp in Etc/GMT+5 (POSIXct)
Instrument      Name of measurement instrument (character)

See #298

[bpbond]

Feedback welcome @stephpenn1

[stephpenn1]

This looks great, and I like the metadata additions. Thank you! This is important metadata to capture explicitly