Need to be able to take a custom composite fides_tc_string and parse out TC and AC strings

[allisonking]

Is your feature request related to a specific problem?

#4262 adds the ability to take in a custom fides_tc_string in order to overwrite initial settings. This string will actually be a composite string, comma separated into {TC_STRING},{AC_STRING} and so we need to be able to handle that.

Describe the solution you'd like

In theory we already have the logic to initialize from TC_STRING, but we'll need to make sure to parse it first. For AC_STRING, we'll likely have to initialize our vendor (and maybe system?) fields anew.

Also, add validation for format of fides_string. We accept TC, TC, and TC,AC, but let's reject ,AC.

Describe alternatives you've considered, if any

A description of any alternative solutions or features you've considered.

Additional context

https://ethyca.atlassian.net/wiki/spaces/PM/pages/2784788587

[eastandwestwind]

Let's think about: when a custom fides_tc_string is passed in, what are the possible states? TC, TC,AC? It won’t be possible to just have AC or ,AC correct?

[NevilleS]

Yeah- just TC, TC, and TC,AC

We can reject ,AC, that's invalid because the core TC string is always needed for a complete signal