Add support for static bearer token authentication for Kubernetes

[simonferquel]

Fix #1852
- What I did

This adds support for importing kubeconfig file using token-based
authentication.

- How I did it

The bearer token is stored within the tls store because of its sensitive
nature.

- How to verify it

Comes with unit tests

[simonferquel]

cc @alexmavr

[codecov-io]

Codecov Report

Merging #1855 into master will increase coverage by 0.03%.
The diff coverage is 89.18%.

@@            Coverage Diff             @@
##           master    #1855      +/-   ##
==========================================
+ Coverage   56.75%   56.79%   +0.03%     
==========================================
  Files         309      309              
  Lines       21658    21687      +29     
==========================================
+ Hits        12292    12317      +25     
- Misses       8469     8471       +2     
- Partials      897      899       +2

[alexmavr]

Thanks for the quick turnaround!

[alexmavr]

I do see the context correctly generated with the following TLSMaterial and a corresponding token file in the TLSPath

        "TLSMaterial": {
            "kubernetes": [
                "token"
            ]
        },

However, trying to deploy a stack returns the following error:

$ docker stack deploy --compose-file docker-compose.yml --orchestrator=kubernetes petstore
WARN[0000] unknown file token in context test-cluster-1 tls bundle 
Unauthorized

[Amos-85]

@simonferquel
There is a merge conflict.
any chance to resolve it ?

This fix is very important for anyone who work with authentication token for k8s clusters.

[Amos-85]

@thaJeztah ,
Will it be possible to support token authentication for k8s builder context ?

[wyrie-zz]

Would be great to have this

[stevefan1999-personal]

can this be revived?