docs: fix timeouts in the health check example and update links for config-default.yaml reference

[kayx23]

Type of change:

• Bugfix
• New feature provided
• Improve performance
• Backport patches
• Documentation
• Refactor
• Chore
• CI/CD or Tests

What this PR does / why we need it:

Encountered errors using the correct example.

Error from server (BadRequest): error when creating "upstreams.yaml": ApisixUpstream in version "v2" cannot be handled as a ApisixUpstream: strict decoding error: unknown field "spec.healthCheck.passive.unhealthy.timeout"

spec.healthCheck.active.timeout: Invalid value: "string": spec.healthCheck.active.timeout in body must be of type number: "string"

This PR fixes the example.

Pre-submission checklist:

• Did you explain what problem does this PR solve? Or what new features have been added?
• Have you added corresponding test cases?
• Have you modified the corresponding document?
• Is this PR backward compatible? If it is not backward compatible, please discuss on the mailing list first

[pottekkat]

Could you check the lint error for the broken link?

It seems like the config-default.yaml file was moved to https://github.com/apache/apisix/blob/master/conf/config.yaml.example and now we define the default config in a Lua file: apache/apisix#11343

It should be a find and replace fix and since the scope of this PR isn't too big, we can fix it here itself.

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