feat(HttpHandler): allow to skip auth on paths via callback

[kostasrim]

• This PR allows the user of HttpListenerBase to register a cb that if it returns true, it will skip the auth.
• Added username_ field to HttpListenerBase such that we can verify against a specific username

@romange I decided to slightly diverge from what we originally discussed, namely that the customization point will be the auth callback. For our use case, we don't really need that, as the only thing we want to do, is to skip the auth part on certain paths. Otherwise, we would need to also expose to the user, functions that deal with parsing of the http protocol and for our use case this is not really needed.

[kostasrim]

The tests that fails is not related, and I see it's been failing for a while...

[romange]

Also, please rebase - the last commit should have fixed the CI

[kostasrim]

Do not merge this, I will reply here once I am sure this works well on dragonfly.

Edit: ALL ok on DF side

[codecov-commenter]

Codecov Report

All modified lines are covered by tests :white_check_mark:

Comparison is base (308aa22) 77.47% compared to head (ee0a5b7) 77.44%.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #150 +/- ## ========================================== - Coverage 77.47% 77.44% -0.03% ========================================== Files 98 98 Lines 7165 7165 ========================================== - Hits 5551 5549 -2 - Misses 1614 1616 +2 ``` [see 3 files with indirect coverage changes](https://app.codecov.io/gh/romange/helio/pull/150/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Roman+Gershman)

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