feat: Allow to force update the internal cache

[thomaspoignant]

Description

This PR adds functionality to force the call to the retrievers when we know that a change has happened in the configuration of your flag, it will call the retrievers without having to wait for the next polling interval to happen.

A good example of when to call this new API?
We set the polling interval to a high value (~15 minutes) BUT in the CI process of our flag config file, we explicitly call a function (or API) to refresh the flags configuration.

In the relay proxy

A new endpoint has been added and allows to force refresh the call to the retrievers.

⚠️ This endpoint requires having an admin token because we want to avoid any DDOS on this endpoint. You need to configure an admin authorized key inside you relay-proxy configuration under the key authorizedKeys.admin.

example:

curl -X 'POST' \
  'http://<your_domain>:1031/admin/v1/retriever/refresh' \
  -H 'accept: application/json' \
  -H 'Authorization: Bearer <your_admin_api_key>' \
  -d ''

In the go module

If you are using the go module, a new function is available and is called ffclient.ForceRefresh().
example:

goff, _ := ffclient.New(ffclient.Config{
	PollingInterval: 10 * time.Minute,
	Retriever: &fileretriever.Retriever{
		Path: "xxxx.yaml",
	},
})

// ...
goff.ForceRefresh()
// ...

⚠️ Deprecations / Breaking changes

Before this version, the way to configure your API Keys for the relay proxy was by setting the key apiKeys in the relay-proxy configuration file.

go-feature-flag/website/docs/relay_proxy/configure_relay_proxy.md

Line 46 in c048469

| `apiKeys` | []string | **none** | List of authorized API keys. Each request will need to provide one of authorized key inside `Authorization` header with format `Bearer <api-key>`.<br /><br />_Note: there will be no authorization when this config is not set._ |

Now this way of configuring the authorized API keys is deprecated and we are using a key called authorizedKeys.

go-feature-flag/website/docs/relay_proxy/configure_relay_proxy.md

Line 46 in 21f58bb

| `authorizedKeys` | [authorizedKeys](#type-authorizedkeys) | **none** | List of authorized API keys. |

go-feature-flag/website/docs/relay_proxy/configure_relay_proxy.md

Lines 54 to 61 in 21f58bb

	## type `authorizedKeys`
	To be able to control who can access your relay proxy, you can set a list of authorized keys.
	| Field name | Type | Default | Description |
	|--------------|----------|----------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
	| `evaluation` | []string | **none** | If set, we will check for each evaluation if an authorized key is provided.<br/>Each request will need to provide one of authorized key inside `Authorization` header with format `Bearer <api-key>`.<br /><br />_Note: there will be no authorization when this config is not set._ |
	| `admin` | []string | **none** | You need to set API keys in this field if you want to access the `/v1/admin/*` endpoints.<br/> If no api key is configured the endpoint will be unreachable.<br/>Each request will need to provide one of authorized key inside `Authorization` header with format `Bearer <api-key>`. |

Closes issue(s)

Resolve #1858

Checklist

• I have tested this code
• I have added unit test to cover this code
• I have updated the documentation (README.md and /website/docs)
• I have followed the contributing guide

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🔨 Latest commit	4344470
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[codecov]

Codecov Report

Attention: Patch coverage is 82.08955% with 24 lines in your changes are missing coverage. Please review.

Project coverage is 86.80%. Comparing base (c048469) to head (4344470).

Files	Patch %	Lines
cmd/relayproxy/api/routes_ofrep.go	35.29%	9 Missing and 2 partials ⚠️
cmd/relayproxy/api/routes_goff.go	41.66%	5 Missing and 2 partials ⚠️
cmd/relayproxy/api/routes_admin.go	57.14%	2 Missing and 1 partial ⚠️
feature_flag.go	80.00%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1878      +/-   ##
==========================================
+ Coverage   86.72%   86.80%   +0.07%     
==========================================
  Files          89       95       +6     
  Lines        3368     3433      +65     
==========================================
+ Hits         2921     2980      +59     
- Misses        345      349       +4     
- Partials      102      104       +2     

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[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud