Support several user configs for taint analysis

[mmvpm]

Description

Now the user can provide their own configuration only using the ./.idea/utbot-taint-config.yaml file.

But sometimes he may want to specify configuration in several files.

Expected behavior

User can specify the directory in the UnitTestBot settings (in IntelliJ IDEA) and put all their own configs there. Maybe it is worth to create a default ./.idea/utbot-taint directory with an empty .yaml config file (if the user checked "Enable taint analysis" checkbox).

Context

See the Taint analysis docs