synthetic data and baselines

[alex2awesome]

Added synthetic data and code for baselines (hft and giantmidi):

• Adds midi-> audio pipeline that randomly picks k of 7 piano-like instruments (piano, harpischord, organ, guitar, etc.) to convert the audio to. Takes the following hyperparameters:
  -> k= # synthetic augmentations to generate
  -> prob distribution= weight to give each instrument
• Adds two baselines (hft and giantmidi) to the baselines folder, as well as cli code to run them

todo after this PR: make pipelines for evaluations:

• maestro -> hft/giantmidi/ours
• augment maestro -> hft/giantmidi/ours
• dtw -> hft/giantmidi/ours

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
1 out of 2 committers have signed the CLA.

✅ loubbrad
❌ Alex Spangher

---

Alex Spangher seems not to be a GitHub user. You need a GitHub account to be able to sign the CLA. If you have already a GitHub account, please add the email address used for this commit to your account.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[loubbrad]

Looks good, just need to remember to run make format for the linter