Add default value "/" for HTTPPathMatch

[nak3]

What this PR does / why we need it:

HTTPPathMatch has a default prefix match on the "/" path.
For example, if match was not configured, the default prefix match with value will be filled.

(This configuration works.)

spec:
  rules:

However, once we added type such as Prefix or Exact, the value
field must be filled by ourselves.

(This configuration does not work due to missing value field.)

spec:
  rules:
    matches:
    - path:
        type: Prefix

Hence this patch adds the default / value for path.value.

What type of PR is this?

/kind api-change

Does this PR introduce a user-facing change?:

HTTPPathMatch path.value sets default value "/" when type was configured but value was not.

[k8s-ci-robot]

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[robscott]

Thanks! This makes sense to me, assigning to @danehans to be sure.

/ok-to-test
/lgtm
/assign @danehans

[danehans]

@nak3 thanks for catching this issue. Since value is being defaulted at higher layers of the API, it should be defaulted and be set to optional directly on the field.

/lgtm when #584 (comment) is resolved.

[robscott]

Thanks!

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: nak3, robscott

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