Replace the 'hash' index with 'tree' in tutorials and examples

Product: Tarantool
Root documents:

• https://www.tarantool.io/en/doc/latest/how-to/app/creating_app/bootstrapping_a_database/
• https://www.tarantool.io/en/doc/latest/how-to/app/creating_app/index_iterators/
• https://www.tarantool.io/en/doc/latest/how-to/getting_started_go/
• https://www.tarantool.io/en/doc/latest/how-to/getting_started_php/
• https://www.tarantool.io/en/doc/latest/how-to/getting_started_python/
• https://www.tarantool.io/en/doc/latest/how-to/getting_started_cxx/
• https://www.tarantool.io/en/doc/latest/how-to/getting_started_net_box/#sandbox-configuration

SME: @ mons

Details

The 'hash' index is described in the documentation as follows:

HASH indexes require unique fields and loses to TREE in almost all respects. So we do not recommend to use it in the applications. HASH is now present in Tarantool mainly because of backward compatibility.

At the same time, it is used in many tutorials and examples. It would be nice to replace its usages with the 'tree' index.

Start with the seven root documents listed in the issue and search their tutorials and examples for uses of the 'hash' index. Replace applicable examples with the 'tree' index, then review each listed page to confirm the examples are consistent with the documented recommendation.