Add non-boolean feature flags support to the StaticProvider (#115085)

* initial commit

* add support of integerts

* finialise the static provider

* minor refactoring

* the rest

* revert:  the rest

* add new thiongs

* more tests added

* add ff parsing tests to check if types are handled correctly

* update tests according to recent changes

* address golint issues

* Update pkg/setting/setting_feature_toggles.go

Co-authored-by: Dave Henderson <dave.henderson@grafana.com>

* fix rebase issues

* addressing review comments

* add test cases for enterprise

* handle enterprise cases

* minor refactoring to make api a bit easier to debug

* make test names a bit more precise

* fix linter

* add openfeature sdk to goleak ignore in testutil

* Remove only boolean check in ff gen tests

* add non-boolean types top the doc in default.ini and doc string in FeatureFlag type

* apply remarks, add docs to sample.ini

* reflect changes in feature flags in the public grafana configuration doc

* fix doc formatting

* apply suggestions to the doc file

---------

Co-authored-by: Dave Henderson <dave.henderson@grafana.com>

docs/sources/setup-grafana/configure-grafana/_index.md

@@ -2836,9 +2836,11 @@ For more information about Grafana Enterprise, refer to [Grafana Enterprise](../
 
 Keys of features to enable, separated by space.
 
-#### `FEATURE_TOGGLE_NAME = false`
+#### `FEATURE_NAME = <value>`
 
-Some feature toggles for stable features are on by default. Use this setting to disable an on-by-default feature toggle with the name FEATURE_TOGGLE_NAME, for example, `exploreMixedDatasource = false`.
+Use a key-value pair to set feature flag values explicitly, overriding any default values. A few different types are supported, following the OpenFeature specification. See the defaults.ini file for more details.
+
+For example, to disable an on-by-default feature toggle named `exploreMixedDatasource`, specify `exploreMixedDatasource = false`.
 
 <hr>