Do not require lr_scheduler for all other recipes

[thomasjpfan]

Context

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• add a new feature
• fix a bug
• update tests and/or documentation
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Fixes #2021. This PR uses the pattern in #1991 for the rest of the recipes.

Changelog

What are the changes made in this PR?

• Allows lr_scheduler to be optional in all recipes.

Test plan

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UX

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[pytorch-bot]

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• [DomainsOnly] Jobs fail with GLIBC version not found

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[felipemello1]

Good stuff! Thanks @thomasjpfan . I can't test it right now, but i will run later something quick for every recipe, just as a sanity check. If there are no issues, i will merge.