fix: loadConfig function should work in browser

[AlexVarchuk]

What/Why/How?

When using loadConfig function to get the config for the browser environment, we get an error: "path.extname is not a function"

Reference

Testing

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• [ ] Code changed? - Tested with Redoc/Realm/Reunite (internal)
• [ ] All new/updated code is covered by tests
• [ ] New package installed? - Tested in different environments (browser/node)

Security

• [x] The security impact of the change has been considered
• [x] Code follows company security practices and guidelines

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: 545c06f8aded99f4fb97eab7e79449bc92569cbe

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

This PR includes changesets to release 3 packages

Name	Type
@redocly/openapi-core	Patch
@redocly/cli	Patch
@redocly/respect-core	Patch

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[github-actions[bot]]

Command	Mean [s]	Min [s]	Max [s]	Relative
redocly lint packages/core/src/benchmark/benches/rebilly.yaml	1.424 ± 0.024	1.381	1.459	1.00
redocly-next lint packages/core/src/benchmark/benches/rebilly.yaml	1.436 ± 0.035	1.390	1.498	1.01 ± 0.03