Add scalability tests to the BMO e2e suite

[dtantsur]

We have scalability tests in CAPM3, but these are less useful for testing Ironic or BMO+Ironic since the entire CAPI machinery can easily become a bottleneck. We can use fake IPA to avoid setting up a lot of virtual machines.

There are a few things we can potentially test:

• How many hosts we can enroll and provision within a certain time window
• How many hosts can exist in Ironic without the API responses falling beyond a certain threshold

[dtantsur]

/kind ci

[Rozzii]

/triage accepted
/@assign @Rozzii @adilGhaffarDev

[metal3-io-bot]

Issues go stale after 90d of inactivity.
Mark the issue as fresh with /remove-lifecycle stale.
Stale issues will close after an additional 30d of inactivity.

If this issue is safe to close now please do so with /close.

/lifecycle stale

[Rozzii]

/remove-lifecycle stale
/priority important-longterm