Receipt files should be named deterministicly

[erichaagdev]

Currently, experiment receipt files are named <short_experiment_name>-<buld_tool>-<timestamp>.receipt.

I see little value in having such an elaborate naming scheme and it makes automation scenarios slightly more challenging.

Instead, the receipt files should be named consistently across all experiments and build tools, like experiment.receipt.

This would make finding the receipt file much easier. For example:

cat .data/01-validate-incremental-building/latest/experiment.receipt

Would always print the receipt for the most recent invocation of experiment 1.

If #619 were implemented, then:

cat .data/latest/experiment.receipt

Would always get you the receipt of the most recent invocation across all experiments.