feat: Angular SDK (#997)

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## This PR
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Adds an Angular SDK as discussed in #976.
It mainly provides directives that conditionally render based on flag
value and provider state.

I did not inject any OpenFeature service or anything like that, as I
think the directives will be the way to access feature flags in the
templates, and the OpenFeature global API can be used directly in
services. But I am not 100% sure on that one.

Happy to receive feedback and opinions :)

A small test app can be found here:
https://github.com/open-feature/angular-test-app
This can be used with [yalc](https://github.com/wclr/yalc).

---------

Signed-off-by: Lukas Reining <[email protected]>
Co-authored-by: Todd Baert <[email protected]>

Author: lukas-reining

.release-please-manifest.json

@@ -1,6 +1,7 @@
 {
   "packages/nest": "0.2.1-experimental",
   "packages/react": "0.4.5",
+  "packages/angular": "0.0.1-experimental",
   "packages/web": "1.2.3",
   "packages/server": "1.15.1",
   "packages/shared": "1.4.0"

jest.config.ts

@@ -189,6 +189,7 @@ export default {
         ],
       },
     },
+    '<rootDir>/packages/angular',
   ],
 
   // Use this configuration option to add custom reporters to Jest