fix(medusa): Throw on flat rate shipping options with no amount

[olivermrbl]

What
When attempting to create or update shipping options of type flat_rate, we should require an amount. This PR throws when not the case.

[changeset-bot]

🦋 Changeset detected

Latest commit: ace0d02

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@medusajs/medusa	Patch

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[adrien2p]

LGTM - only a few comments. Also, I see that it does not only includes the flat rate issue anymore :) We might need to change the description of that pr

[pKorsholm]

Generally I think it looks good.

+1 on @adrien2p's comment regarding pass-by-reference 😄

[adrien2p]

LGTM. Just need the pipeline to finish

[gitguardian]

⚠️ GitGuardian has uncovered 2 secrets following the scan of your pull request.

Please consider investigating the findings and remediating the incidents. Failure to do so may lead to compromising the associated services or software components.

🔎 Detected hardcoded secrets in your pull request

GitGuardian id	Secret	Commit	Filename
5067995	Company Email Password	c46f0a4	packages/medusa/src/services/tests/customer.js	View secret
5165075	Company Email Password	c46f0a4	packages/medusa/src/api/routes/store/customers/tests/reset-password.js	View secret

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[srindom]

LGTM!