Move OIDC Provider list to be publicly accessible

[jvanderhoof]

Desired Outcome

This PR changes the OIDC redirect API to be publicly accessible. This is ok from a security perspective as it only contains the information that would be included on a login page using one of the OIDC Authenticators.

Implemented Changes

Remove authentication requirements from the Providers endpoint.

Connected Issue/Story

N/A

Definition of Done

At least 1 todo must be completed in the sections below for the PR to be
merged.

Changelog

• The CHANGELOG has been updated, or
• This PR does not include user-facing changes and doesn't require a
  CHANGELOG update

Test coverage

• This PR includes new unit and integration tests to go with the code
  changes, or
• The changes in this PR do not require tests

Documentation

• Docs (e.g. READMEs) were updated in this PR
• A follow-up issue to update official docs has been filed here: insert issue ID
• This PR does not require updating any documentation

Behavior

• This PR changes product behavior and has been reviewed by a PO, or
• These changes are part of a larger initiative that will be reviewed later, or
• No behavior was changed with this PR

Security

• Security architect has reviewed the changes in this PR,
• These changes are part of a larger initiative with a separate security review, or
• There are no security aspects to these changes

[codeclimate]

Lists should be surrounded by blank lines

[codeclimate]

Code Climate has analyzed commit 0ca31ba and detected 1 issue on this pull request.

Here's the issue category breakdown:

Category	Count
Style	1

The test coverage on the diff in this pull request is 100.0% (50% is the threshold).

This pull request will bring the total coverage in the repository to 90.0% (-1.5% change).

View more on Code Climate.

[mFelgate]

lgtm