Add support for apps webhook config endpoints

[rpelliard]

This adds support for two Apps API endpoints (see #2095)

• Get a webhook configuration for an app
• Update a webhook configuration for an app

Both endpoints require authentication as an app (with a JWT), which can be dealt with by the underlying transport.

A few notes:

• I reused / extended the HookConfig struct which was defined in orgs_audit_logs.go, since it represents the same object.

• The InsecureSSL field of the struct is a *string. However, GitHub only returns "0" or "1" (insecure SSL disabled / enabled), so I think it'd be more user-friendly to use a *bool, and write some logic so that boolean values are correctly (un)marshaled from "0"/"1". I'd be happy to write the code to deal with this, but that would be a breaking change so I wanted to check with you first.

• This is probably out of scope of this PR, but the Hook struct used for repository / organization webhooks endpoints is using a map[string]interface{} for the Config field, but I think it could be using the HookConfig struct as well since it represents the same object. Happy to make that change in a separate PR, but this would be a breaking change as well.

[codecov]

Codecov Report

Merging #2096 (def1026) into master (33ae6f3) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head def1026 differs from pull request most recent head e18619d. Consider uploading reports for the commit e18619d to get more accurate results

@@           Coverage Diff           @@
##           master    #2096   +/-   ##
=======================================
  Coverage   97.77%   97.78%           
=======================================
  Files         109      110    +1     
  Lines        9724     9746   +22     
=======================================
+ Hits         9508     9530   +22     
  Misses        150      150           
  Partials       66       66           

Impacted Files	Coverage Δ
github/orgs_audit_log.go	100.00% <ø> (ø)
github/apps_hooks.go	100.00% <100.00%> (ø)

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[gmlewis]

Thank you, @rpelliard !
One tiny nit to fix, please, but otherwise LGTM.

Awaiting second LGTM before merging.

[gmlewis]

LGTM.

Awaiting second LGTM before merging.

[rpelliard]

Hello @gmlewis @wesleimp, do you know when we'd be able to merge this ?

[gmlewis]

Hello @gmlewis @wesleimp, do you know when we'd be able to merge this ?

Maybe @Parker77 has time to take a look at this one.

[Parker77]

One minor nit, otherwise LGTM.

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[Parker77]

@googlebot I fixed it.

[gmlewis]

One minor nit, otherwise LGTM.

Thank you, @Parker77 !
Merging.