HIVE-29020: OAuth 2 support with Keycloak example

[okumin]

Document about apache/hive#6086.

How I tested.

docker run --rm -it \
  -v $(pwd):/src \
  -p 1313:1313 \
  klakegg/hugo:0.91.2 \
  server

http://localhost:1313/docs/latest/admin/oauth2/
http://localhost:1313/docs/latest/admin/oauth2/keycloak/

[okumin]

@deniskuzZ I drafted some documents

[deniskuzZ]

@okumin, nice! I think next step would be to add OAuth 2 support for Hive RestCatalog client: HIVE-29234.
Could we borrow the code from Trino :) ?

[deniskuzZ]

+1

[okumin]

@deniskuzZ I would say we can use iceberg-core as it is. I'll check if we need to implement anything additional.