The auto-increment feature for multipart PK

[TarantoolBot]

The auto-increment feature can be set to any INTEGER or UNSIGNED
field of PRIMARY KEY using one of two ways:

1. AUTOINCREMENT in column definition:
   CREATE TABLE t (i INT, a INT AUTOINCREMENT, PRIMARY KEY (i, a));
   CREATE TABLE t (i INT AUTOINCREMENT, a INT, PRIMARY KEY (i, a));
2. AUTOINCREMENT in PRIMARY KEY definition:
   CREATE TABLE t (i INT, a INT, PRIMARY KEY (i, a AUTOINCREMENT));
   CREATE TABLE t (i INT, a INT, PRIMARY KEY (i AUTOINCREMENT, a));
   Requested by @ImeevMA in tarantool/tarantool@08c7d7c.

[pgulutzan]

SQL constraint definitions will be published when approved.

[veod32]

Do we have the description of this feature in our 2.3 documentation? 08c7d7c commit that closes the feature ticket gh-4217 is in the 2.3.1 release scope already.

[pgulutzan]

That part of the documentation has not been approved. Perhaps K. Yukhin knows whether or not it will be approved.

[Totktonada]

@pgulutzan, can you share the commit? I guess I can review it from correctness point of view and it is enough for now.

I'll ask help from @artembo to push it in the right way (same as for #879).