[http plugin] Add capath, certpath, keypath to load custom certs

[LaurenceJJones]

Implement #2142

I can replicate these changes across to other plugins that use http base stuff, However, I wanted to draft a PR to ask should we include the helpers function in go-cs-lib as then we can have a central place tag @mmetc

[github-actions]

@LaurenceJJones: There are no 'kind' label on this PR. You need a 'kind' label to generate the release automatically.

• /kind feature
• /kind enhancement
• /kind fix
• /kind chore
• /kind dependencies

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[github-actions]

@LaurenceJJones: There are no area labels on this PR. You can add as many areas as you see fit.

• /area agent
• /area local-api
• /area cscli
• /area security
• /area configuration

Details

I am a bot created to help the crowdsecurity developers manage community feedback and contributions. You can check out my manifest file to understand my behavior and what I can do. If you want to use this for your project, you can check out the BirthdayResearch/oss-governance-bot repository.

[LaurenceJJones]

/kind enhancement
/area agent

[codecov]

Codecov Report

Attention: 54 lines in your changes are missing coverage. Please review.

Comparison is base (acd2a14) 55.01% compared to head (0aa659a) 55.04%.

Files	Patch %	Lines
cmd/notification-http/main.go	0.00%	54 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2634      +/-   ##
==========================================
+ Coverage   55.01%   55.04%   +0.02%     
==========================================
  Files         220      224       +4     
  Lines       29421    29841     +420     
==========================================
+ Hits        16187    16425     +238     
- Misses      11663    11811     +148     
- Partials     1571     1605      +34     

Flag	Coverage Δ
bats	36.41% <0.00%> (-0.11%)	⬇️
unit-linux	49.64% <ø> (+<0.01%)	⬆️
unit-windows	47.77% <ø> (?)

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[mmetc]

Mmmh.. I think the function is simple and idiomatic enough that it doesn't justify the added dependency.