chore(e2e): pin gkg chart 2.0.0 and keep one universal indexer pool

What does this MR do and why?

The e2e suite pinned gkg chart 1.7.0, and the chart line moved to 2.x with a flat secrets shape and split indexer pools. This bumps the pin to 2.0.0 and keeps one universal indexer pool, so the suite stays sized for a single indexer deployment and the health-check targets keep their names.

Related Issues

Relates to #1084 (closed) (the HA variant needs a value that only 2.x charts render).

Testing

Rendered the gkg release offline with helmfile template against chart 2.0.0: 19 resources, the indexer deployment is still gkg-indexer-default, and the engine, schedule, and pipeline overrides render unchanged. The e2e job on this MR passed: https://gitlab.com/gitlab-org/orbit/knowledge-graph/-/jobs/16457385369.

Performance Analysis

None.

• This merge request does not introduce any performance regression. If a performance regression is expected, explain why.