Add support for arrays in tjson

[rumyantseva]

In Tigris, arrays are defined according to the schema. All values of the array have the same type defined in the schema.

In this task we add support of arrays to tjson and write unit tests to check that they work correctly. The full enablement of Tigris arrays will be handled in #1704.

Definition of done

• No TODOs mentioning this issue are left in the code
  • If it's impossible to support what todo is for, change this TODO to mention Enable support for arrays in Tigris #1704 instead.
• Add unit tests (use pjson as a reference):
  • unit tests for arrays in tjson/array_test.go;
  • array examples in tjson/document_test.go.

[rumyantseva]

This task needs a better description and a decision about how to deal with arrays.

[rumyantseva]

TODO: split the task (unit / integration), so we can estimate it better