fix: check for presence of metadata.allowlist instead of allowlist

[Jipperism]

reverts a regression introduced in commit
4f6beba where we started checking for allowlist, instead of metadata.allowlist. We should actually check for the presence of metadata.allowlist, to prevent the case where the user specifies both a CID and a json allowlist to the endpoint.

[github-actions]

Coverage Report

Status	Category	Percentage	Covered / Total
🟢	Lines	20.86% (🎯 20%)	858 / 4113
🟢	Statements	20.86% (🎯 20%)	858 / 4113
🟢	Functions	52.85% (🎯 52%)	37 / 70
🟢	Branches	67.96% (🎯 63%)	140 / 206

File Coverage

File	Stmts	Branches	Functions	Lines	Uncovered Lines
Changed Files
src/controllers/MetadataController.ts	41.37%	72.72%	50%	41.37%	61-73, 116-180, 214-228, 237-244, 261-308

Generated in workflow #39 for commit 61ac0c3 by the Vitest Coverage Report Action

[Jipperism]

Closes hypercerts-org/hypercerts-app#360