[confighttp] Use configoptional.Optional for optional fields

[mx-psi]

Description

Makes the following changes to confighttp:

1. Uses configoptional.Optional in confighttp for all optional sections

This means a bunch of breaking changes. I think it is unfeasible to do this in two steps and I hereby promise that I will fix contrib tests and help anybody affected by this

Link to tracking issue

Fixes #9478

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.60%. Comparing base (633b6de) to head (b8a4d7a).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #13109   +/-   ##
=======================================
  Coverage   91.59%   91.60%           
=======================================
  Files         506      506           
  Lines       28534    28537    +3     
=======================================
+ Hits        26137    26140    +3     
  Misses       1882     1882           
  Partials      515      515           

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[mx-psi]

I split off a couple of changes into separate PRs since those are clearer to me:

• [confighttp,configgrpc] Rename TLSSetting to TLS #13115
• [confighttp] Remove pointer in CookiesConfig field #13116

[mx-psi]

Also, since I guess it is clear that configoptional.Optional is a good fit for the OTLP receiver I will start with that one.