Support custom processing and mapping per test

[jsoriano]

There are some integrations, specially generic ones, that are expected to be used with custom mappings.

Support defining custom ingest pipelines and custom mappings per test, so these use cases can be validated. These customizations could be defined directly in configuration files of the tests, or referenced from there.

See for example this conversation, where it is mentioned that some mappings are added to the package itself only to avoid having undocumented fields in test cases.