Clean up HTTP authentication reference and Update constructors

[programbeginnerTW]

1. Clean up HTTP authentication reference
2. Update constructors in JiraSite.java and JireSiteTest.java
3. Leave the @Deprecated annotation in case any error should occur

• [x] Make sure you are requesting to pull a topic/feature/bugfix branch (right side) and not your master branch!
• [x] Ensure that the pull request title represents the desired changelog entry
• [x] Please describe what you did

[programbeginnerTW]

Is there anything I should do toward this pull request? @rantoniuk

[olamy]

I don't remember if this is serialized or not? because changing a field will break existing configuration

[rantoniuk]

@olamy correct me if I'm wrong, but from what I remember, everything that is not @transient is serialized when JiraSite is saved.

So we would need to:

• deprecate the constructor and the field that we want to drop + make that field transient
• release that
• and afterwards in the next release cycle drop everything

(or alternatively again write some "migrator" that we did already in the past, but I'm just looking for a simpler solution..) When I have some time, I'll try to run some local tests to see which approach works, but maybe you already know what to suggest.