[FEATURE] Add Blockgroups to MGRA table

[GregorSchroeder]

Is your feature request related to a problem? Please describe

In order to create estimates of self-employed individuals we use ACS 5-year data at the blockgroup level and distribute down to MGRAs.

Describe the solution you'd like

Add the [2010_census_blockgroup] and [2020_census_blockgroup] geographies to the [inputs].[mgra] table. There are already populated Series 15 MGRA cross references to both geographies present in the [GeoAnalyst] database.

Describe alternatives you've considered

We could consider sticking to the Census Tract level but that is currently only done when we are applying distributions to counts that we generate from other sources. In this instance it is the ACS itself driving the counts, so it is probably more appropriate to use the more granular geographic level.

Additional context

See #200