🌱 Add unit test for LoadAuth funciton in auth.go

[babugeet]

What this PR does / why we need it:

This PR adds unit test for LoadAuth funciton, mentioned in the issue #1574

Which issue(s) this PR fixes:
Fixes # #1574

The provided test cases cover the following scenarios for the LoadAuth function:

No Authentication Directory Exists:
    Test Case: NoAuthDirectory
    Description: Tests the scenario where the ironic authentication directory does not exist. The function should return NoAuth as the authentication type without any errors.

Valid Authentication Credentials:
    Test Case: ValidAuth
    Description: Tests the scenario where the ironic directory exists with valid username and password files. The function should return HTTPBasicAuth with the correct username and password.

Empty Username File:
    Test Case: EmptyUsername
    Description: Tests the scenario where the username file is present but empty. The function should return an error indicating that the HTTP Basic Auth username is empty.

Empty Password File:
    Test Case: EmptyPassword
    Description: Tests the scenario where the password file is present but empty. The function should return an error indicating that the HTTP Basic Auth password is empty.

[babugeet]

/cc @lentzi90 @kashifest

[lentzi90]

Thank you! The code looks good!
Could you please squash the commits?
/approve

/hold
(for squashing)

[metal3-io-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: lentzi90

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[babugeet]

@lentzi90 : commits are squashed.
Pls check

[kashifest]

/ok-to-test
@babugeet you need to fix DCO complain as well, just sign the commit with -S , check this section for reference.

[babugeet]

@kashifest : the DCO and the lint issues are solved.
Lint issue fix have added one more commit, do i need to squash that commit

[lentzi90]

Yes please squash always

[kashifest]

@kashifest : the DCO and the lint issues are solved. Lint issue fix have added one more commit, do i need to squash that commit

Thanks. ideally yes squashed with a proper commit message would be helpful

[babugeet]

@lentzi90 , @kashifest : addressed all comments. Pls check

[kashifest]

/lgtm

[kashifest]

/hold cancel