Fixes
- https://github.com/linkerd/linkerd2/issues/2962
- https://github.com/linkerd/linkerd2/issues/2545
### Problem
Field omissions for workload objects are not respected while marshaling to JSON.
### Solution
After digging a bit into the code, I came to realize that while marshaling, workload objects have empty structs as values for various fields which would rather be omitted. As of now, the standard library`encoding/json` does not support zero values of structs with the `omitemty` tag. The relevant issue can be found [here](https://github.com/golang/go/issues/11939). To tackle this problem, the object declaration should have _pointer-to-struct_ as a field type instead of _struct_ itself. However, this approach would be out of scope as the workload object declaration is handled by the k8s library.
I was able to find a drop-in replacement for the `encoding/json` library which supports zero value of structs with the `omitempty` tag. It can be found [here](https://github.com/clarketm/json). I have made use of this library to implement a simple filter like functionality to remove empty tags once a YAML with empty tags is generated, hence leaving the previously existing methods unaffected
Signed-off-by: Mayank Shah <mayankshah1614@gmail.com>
* Add inject support for namespaces(Fix#3255)
* Add relevant unit tests (including overridden annotations)
Signed-off-by: Mayank Shah <mayankshah1614@gmail.com>
Mayank Shah