[SQL] change catalog references to datasource.

[vmmusings]

Is your feature request related to a problem?
We are going ahead with datasource name instead of catalog. The ask from this issue is to rename all the references of catalog to datasource.

What solution would you like?
A clear and concise description of what you want to happen.

What alternatives have you considered?
A clear and concise description of any alternative solutions or features you've considered.

Do you have any additional context?
Add any other context or screenshots about the feature request here.

[Yury-Fridlyand]

Why not schema to comply with other DBs?

[vmmusings]

schema represents group of tables under a datasource.

datasource --> schema --> table is the heirarchy.

In order to not conflict with this project: https://github.com/opensearch-project/opensearch-catalog/blob/main/docs/catalog-rfc.md

we are changing catalog to datasource.

[Yury-Fridlyand]

Thank you for clarifying details!