fix:allow to only override elevated limits but merging with original config

[pubalokta]

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Description

Fixes an error we found when providing overrides.

Problem detected: If we only provided overrides for elevated_limits, with no override for base size and/or per_x, the final configuration would not include the size and per_x.

Example:

• Base bucket config

buckets = {
   ip: {
      size: 10,
      per_second: 5,
      overrides: {
         'awesome-key': {
            elevated_limits: {
               size: 200,
               per_second: 200,
            }
         }
      }
   }
}

When the override is processed, the configuration of the limit for 'awesome-key' results in:

'awesome-key': {
    elevated_limits: {
       size: 200,
       per_second: 200,
    }
 }

This means that the base size and per_x for that key are undefined which causes an internal error.

Solution
The solution is merging the override with the base configuration. If the override includes elevated configuration but NO base configuration it gets merged, resulting in:

'awesome-key': {
    size: 10,
    per_second: 5,
    elevated_limits: {
       size: 200,
       per_second: 200,
    }
 }

References

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Checklist

• I have added documentation for new/changed functionality in this PR or in auth0.com/docs
• All active GitHub checks for tests, formatting, and security are passing
• The correct base branch is being used, if not the default branch