Move datetime formatting to Datetime LogicalType

[tamargrey]

closes #198

Removes 'datetime_format' from config and adds a datetime_format to the Datetime logical type so that any different formats can be indicated for each column.

[codecov]

Codecov Report

Merging #216 into main will decrease coverage by 0.04%.
The diff coverage is 96.96%.

@@            Coverage Diff             @@
##             main     #216      +/-   ##
==========================================
- Coverage   99.86%   99.82%   -0.05%     
==========================================
  Files          22       22              
  Lines        2218     2224       +6     
==========================================
+ Hits         2215     2220       +5     
- Misses          3        4       +1     

Impacted Files	Coverage Δ
woodwork/config.py	100.00% <ø> (ø)
woodwork/tests/data_column/test_data_column.py	100.00% <ø> (ø)
woodwork/logical_types.py	96.15% <80.00%> (-1.11%)	⬇️
woodwork/data_column.py	100.00% <100.00%> (ø)
woodwork/data_table.py	100.00% <100.00%> (ø)
woodwork/tests/data_table/test_datatable.py	100.00% <100.00%> (ø)

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[thehomebrewnerd]

@tamargrey I didn't review this in detail, but we will also want to update the new config options guide in the docs to remove the references to the global datetime format config variable. We will probably also want to include some documentation on how to work with logical types that have options specified, but that can be a separate issue and PR (we will also need this for Ordinal and other logical types that will eventually take options)

[gsheni]

Just minor things. Looks good overall.