[API PULL] Backbone for SYNC endpoint

[puntope]

Changes proposed in this Pull Request:

This is a preparatory PR for the work related to creating a WPCOM Proxied endpoint allowing to GET and UPDATE the enabled Sync mode.

In this PR we create a backbone for the endpoint getting a default value or the value saved in wp_options.gla_api_pull_sync_mode

PT: pcTzPl-2yG-p2

Screenshots:

Detailed test instructions:

1. Request GET wp-json/wc/gla/sync
2. See you get the default response

'products' => [
			'pull' => false,
			'push' => false,
		],
		'coupons'  => [
			'pull' => false,
			'push' => false,
		],
		'shipping' => [
			'pull' => false,
			'push' => false,
		],
		'settings' => [
			'pull' => false,
			'push' => false,
		],

3. Update wp_options.gla_api_pull_sync_mode and save some data for example this with all true:
   a:4:{s:8:"products";a:2:{s:4:"push";b:1;s:4:"pull";b:1;}s:7:"coupons";a:2:{s:4:"push";b:1;s:4:"pull";b:1;}s:8:"shipping";a:2:{s:4:"push";b:1;s:4:"pull";b:1;}s:8:"settings";a:2:{s:4:"push";b:1;s:4:"pull";b:1;}}
4. Perform the request in step 1 again. And see the expected result

Additional details:

Changelog entry

[codecov]

Codecov Report

Attention: Patch coverage is 33.92857% with 37 lines in your changes missing coverage. Please review.

Project coverage is 67.1%. Comparing base (b04c648) to head (641e06c).

Files with missing lines	Patch %	Lines
...rc/API/Site/Controllers/RestAPI/SyncController.php	32.7%	37 Missing ⚠️

Additional details and impacted files

@@                         Coverage Diff                         @@
##             feature/api-pull-sync-endpoint   #2788      +/-   ##
===================================================================
+ Coverage                              66.7%   67.1%    +0.4%     
- Complexity                                0    4684    +4684     
===================================================================
  Files                                   316     481     +165     
  Lines                                  4921   19625   +14704     
  Branches                               1204       0    -1204     
===================================================================
+ Hits                                   3282   13174    +9892     
- Misses                                 1502    6451    +4949     
+ Partials                                137       0     -137     

Flag	Coverage Δ
js-unit-tests	?
php-unit-tests	67.1% <33.9%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...ernal/DependencyManagement/RESTServiceProvider.php	100.0% <100.0%> (ø)
...rc/API/Site/Controllers/RestAPI/SyncController.php	32.7% <32.7%> (ø)

... and 795 files with indirect coverage changes

[mikkamp]

Thanks for the changes, they are working as expected and I'm getting the response either from the defaults or the option.

I just left a couple comments, let me know if you think that would be worthwhile to do.

[mikkamp]

Considering that we only want these endpoints accessible by the API Pull implementation. In the WC endpoints we check for the gla_syncable parameter being set to 1 in the request before we modify the responses.

Should we have a custom permissions callback to also check if this is set? Not very difficult to get around, but it might provide better separation.

[puntope]

Thanks I will update that in future PRs if that's ok

[mikkamp]

Thanks for the changes. I retested and it's return a hybrid of the option and defaults. So everything is as expected:

{
    "products": {
        "push": true,
        "pull": true
    },
    "coupons": {
        "push": false,
        "pull": false
    },
    "shipping": {
        "push": true,
        "pull": true
    },
    "settings": {
        "pull": false,
        "push": false
    }
}