feat(apiovh): handle credentials template

[wI2L]

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

Fix.
Handle the cas where the apiovh plugin's config field credentials is a template.

• What is the current behavior? (You can also link to an open issue here)

Whether the field is a plain string or a template, the validConfig is used to check if the configuration item exists and it valid. During the validation, the config field is not templated yet, resulting in an incorrect value.

• What is the new behavior (if this is a feature change)?

If the config field credentials is a templaate, skip the actual validation process.

• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)

No, the behavior stay the same for current usage.