Decide on when and where we would like to do "official" benchmark runs.

[hodgestar]

The official benchmarks runs are those that are saved to S3 and viewable on qutip.org/qutip-bencmark. Some examples we have discussed:

• On each commit to dev.major (i.e. v5) on the qutip repository.
• Nightly on qutip-benchmark against dev.major

We might also want to do some historical runs, e.g.:

• A historical run against all merge commits from the last year of qutip/master (i.e. v4).

These historical runs we can implement later though.

[xspronken]

I believe this was sorted in #10, when we separated the workflows into 2, one for the nightly benchmarks and one to test new commits and PRs.