Add asv-based performance benchmarks

[sdrave]

This PR adds a basic asv setup with a few benchmarks. I intend to run these benchmarks periodically on a dedicated server for all new merge commits on main. The results will be automatically pushed to

https://docs.pymor.org/asv

At the moment, this is still happening manually.

Todo

• developer documentation
• more benchmarks

[sdrave]

@pymor/main please see if you want to add a few more tests here, in particular in view of #2405.

Note: as this branch is also named 'asv', each successful ci build of the documentation will overwrite docs.pymor.org/asv. Ping me, if you want an update. I will setup continuous tests once this pr has been merged.

[pmli]

@sdrave I've added benchmarks for BT and IRKA. Let me know if it looks ok.