@W-22809731: fix lightningOutApp directoryName to plural

[akashdhake]

What does this PR do?

Corrects the LightningOutApp registry entry's directoryName from the singular lightningOutApp to the
plural lightningOutApps, aligning the SDR registry with the directory name used by Core and required by
the Lightning Out 2.0 DX Requirements (§4.2).

What issues does this PR fix or reference?

@W-22809731@

Aligns SDR with Core PR #29387, where the SDR/Core directory-name mismatch (singular lightningOutApp vs.
plural lightningOutApps) was identified as a blocker for LightningOutApp Metadata API enablement.

Functionality Before

With the default registry (directoryName: lightningOutApp, singular), LightningOutApp could not be retrieved or deployed via DX. sf project retrieve start --metadata LightningOutApp:InstalledPkgApp returned status: 0 with 0 files - the singular directory name didn't match the server's lightningOutApps/ path, so nothing resolved to source.

Functionality After

SDR retrieve/deploy uses force-app/main/default/lightningOutApps/, matching Core.

Metadata Registry: Successful Deploy and Retrieve (required if applicable)

Deploy output:

Retrieve output:

[salesforce-cla]

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