Backport of pki health-check fails to read in int config values into release/1.13.x

[hc-github-team-secure-vault-core]

Backport

This PR is auto-generated from #19265 to be assessed for backporting due to the inclusion of the label backport/1.13.x.

The below text is copied from the body of the original PR.

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Issue Description

While testing the vault pki health-check feature, providing it a configuration file with integer value of say 100 for root_issued_leaves.root_issued_leaves led to the following error.

Failed to build health check configuration: error saving merged config for root_issued_leaves: error parsing root_issued_leaves.certs_to_fetch: could not parse value from input

Fix

• Go's default behavior when decoding numbers to an interface{} is to use a float64 type which parseutil.SafeParseIntRange does not handle. Switch to having the JSON decoder use json.Number which parseutil methods properly handle.
• Tested configuration values as strings, integers work
• Also tested we get proper error messages for out of bounds integers and float values

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Overview of commits

• 4ea5c58