Add 'bluecat' as possible option to the provider flag

[brross]

'bluecat' was missing from the enumerated list of possible values for the provider flag

Description
Add bluecat as a valid provider option to the provider flag.

Although bluecat had previously been added to the descriptive help text for the provider flag it was not included in the enumerated list of acceptable values.

Fixes #2034

Checklist

• [n/a] Unit tests updated
• [n/a] End user documentation updated

[k8s-ci-robot]

Welcome @brross!

It looks like this is your first PR to kubernetes-sigs/external-dns 🎉. Please refer to our pull request process documentation to help your PR have a smooth ride to approval.

You will be prompted by a bot to use commands during the review process. Do not be afraid to follow the prompts! It is okay to experiment. Here is the bot commands documentation.

You can also check if kubernetes-sigs/external-dns has its own contribution guidelines.

You may want to refer to our testing guide if you run into trouble with your tests not passing.

If you are having difficulty getting your pull request seen, please follow the recommended escalation practices. Also, for tips and tricks in the contribution process you may want to read the Kubernetes contributor cheat sheet. We want to make sure your contribution gets all the attention it needs!

Thank you, and welcome to Kubernetes. 😃

[brross]

/cc @seanmalloy @vinny-sabatini

[seanmalloy]

@brross thanks for fixing this!

/lgtm
/kind bug
/assign @njuettner @Raffo

[Raffo]

/approve
/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: brross, Raffo, seanmalloy

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [Raffo]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment