feat: add deploy size and count warnings

[shetzel]

What does this PR do?

Adds a warning when deploy size or deploy file count exceeds a threshold. By default the threshold is 80% of the maximum MDAPI limit.

What issues does this PR fix or reference?

@W-16489032@

To QA:
export DEBUG=sf:MetadataApiDeploy and SF_LOG_LEVEL=debug to see debug output around deploy limits
deploy metadata to a scratch org (dreamhouse-lwc can be used as the project). If you use the --verbose flag it will output the deploy size and count
Override the SF_DEPLOY_SIZE_THRESHOLD env var with different numbers to see changes. 100 or over will disable warnings. 0 will always show warnings. In between, it depends on the amount of metadata being deployed.

[WillieRuemmele]

QA Notes

---

✅ : set env, saw warning Warning: Deployment zip file count is approaching the Metadata API limit (10,000). Warning threshold is 1% and count 111 > 100
✅ : set level = 100, no warning
✅ : level = 2, no warning