Add constant or convinience methods for creating Conditions with PK.

[vrogach2020]

For example now I need to write

Conditions.indexEquals(0, indexParts)
Conditions.indexEquals(TarantoolIndexQuery.PRIMARY, indexParts)

It's not obvious that I should use constants from TarantoolIndexQuery class as well that constant value must be 0 (not 1). I suggest to imrove the Conditions class API to make the following possible:

Conditions.indexEquals(Conditions.PK_INDEX, indexParts)
Conditions.primaryIndexEquals(indexParts)

[akudiyar]

Checklist:

• [ ] Unit tests
• [ ] Add to documentation