CI: Introduce representative benchmarks pipeline

In the past there was daily benchmarks pipeline that collected metrics from the e2e tests and analyzed them for regression.

In practice it was ignored for a long time, likely because the load was non-representative.

Challenge

Find representative load:

• Hard to simulate real load unless on the testnet/mainnet.
• What is relevant load? Checkpoints sync, genesis sync or sync 3 months of data?
  • The relevant load should test more then just storage sync...
• Automatic genesis sync would be nice to see if anything is breaking but this would take too much time.
• How performant are current CI runners? Probably we would need custom bare metal instance for it...

Proposed solution

Have a weekly pipeline or on release pipeline, that triggers representative load and also implicitly checks breaking changes.

E.g. sync 3 most recent months of the data and collect and compare the actual metrics, between the pipeline runs.

https://github.com/oasisprotocol/oasis-core/issues/6423 enables this, whilst https://github.com/oasisprotocol/oasis-core/issues/6422 may define an upper bound for the sync age.

Start by reviewing the existing daily benchmarks pipeline and the e2e tests that currently collect metrics. Use issues #6423 and #6422 to understand the proposed sync capability and age limit, then define a representative load and whether it runs weekly or on releases. Done means the pipeline runs the selected sync, collects comparable metrics, and checks for regressions or breaking changes.