Apply prewarm when benchmarking

[t0yv0]

Wanted to make a couple of changes to improve benchmarking cron. As part of this, realized that the use cases for the test cron and benchmarking cron are diverging so I factored them out into separate code paths for easier reading.

Changes:

• prewarm phase to rule out any further/late plugin installation
• separate SKIP config, skip static-website templates for now
• use dev versions of Pulumi CLI instead of release versions; faster feedback
  • had to roll this back since with bors changes in p/p we do not have a usable "dev" pointer at the moment
• remove parallelism from benchmarks to get better numbers
• higher duration of aws token session to compensate for longer runtimes and avoid failures to upload data

Also I've gotten to the bottom of PULUMI_TEMPLATE_LOCATION use I think - if unset, this tests released templates, but if set to PWD it uses locally modified copies. This is setup just fine on CI but is confusing locally when trying to test out template changes on my machine, by default the tests just ignore those changes unless I remember to set this env var. I've setup convenient make targets and documented this detail, but there's no changes to how CI runs things with respect to this env var.

[t0yv0]

Test run https://github.com/pulumi/templates/actions/runs/3053618633

[t0yv0]

Prewarm + no parallelism makes it take a lot more time but I feel it is worth it. The numbers popping out are smaller again, and hopefully the variance will be smaller also, making them much more useful to us.

[RobbieMcKinstry]

Nice! I left a few comments at your discretion.

[t0yv0]

@lblackstone adding in case you can represent providers team here - editing shared code, wanted to make sure it's ok.

[lblackstone]

LGTM