api: do not require sudo for GetAuth wrapper

[fairclothjm]

This PR proposes the following changes

• remove sudo requirement for GetAuthWithContext and GetAuth API wrapper methods
• add the missing sudo requirement to the API docs for sys/auth/:path

This should allow the TFVP to use the API wrapper and remove the sudo requirement for managing auth methods.

See

• auth/mount: fetch single vault resource on read terraform-provider-vault#2145 (comment)

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CI Results:
All Go tests succeeded! ✅

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