tests: add basic auth mtls tests

[NyaliaLui]

Cover Letter

The HTTP Proxy and Schema Registry now support HTTP Basic Authentication since v22.3.1. This PR tests those services when:

1. mTLS is the only authentication method
2. mTLS and Basic Auth are enabled together

Fixes #6763

#7361 needs to be merged first

Changes from force-push 8c51d9c:

• Add mtls tests for the Schema Registry

Backports Required

• [x] none - not a bug fix
• [ ] none - issue does not exist in previous branches
• [x] none - papercut/not impactful enough to backport
• [ ] v22.3.x
• [ ] v22.2.x
• [ ] v22.1.x

UX Changes

• none

Release Notes

• none

[graphcareful]

Take a look at CI, looks like all of the acl_tests are failing

[NyaliaLui]

@BenPope @graphcareful how do you feel about making this PR the main one so I can just close #7361. That was intended to be the parent PR but it looks like it's unnecessary.

[NyaliaLui]

/ci-repeat 5

[NyaliaLui]

Ci Failures are Non-blockers: #7043

Looks like docker failed to create the debug builds though.