Update README and remove feature gates related to protocol request support once it lands in Lens

[stefcameron]

This is the Lens issue tracking implementation: lensapp/lens#1288

Search the code for this issue here to find the places where things need a bit of refactoring to be made more "official".

For now, the feature gates should(tm) start working once Lens supports the feature.

• Remove feature gates
• Add info in the README about what type of requests are supported
• Update version "4.1" to "4.2" in the "Links" text rendered in the right hand panel in the extension itself

[stefcameron]

lensapp/lens#1288 will be in Lens 4.2 🎉

[stefcameron]

README content to add to "Help" section:

### Supported protocol requests

[Lens 4.2](https://medium.com/k8slens/lens-4-2-released-f1c3268d3f95) introduced a new __custom Lens protocol handler__. This means Lens can now respond to `lens://` URL requests made in the browser, and this extension can now support some interesting requests that enable tighter integration between Mirantis Container Cloud instances and Lens.

> Note that this integration is a one-way street: Container Cloud -> Lens. It does not work the other way around. _Reverse_ integration is achieved simply by making Container Cloud API requests from Lens, which is much easier to achieve, and has been used by this extension since its inception.

The __base URL__ for requests that this extension can respond to is:

```
lens://extensions/@mirantis/lens-extension-cc
```

The following APIs are currently supported by this extension, from the base URL above:

#### Activate cluster

Activates a cluster __already added__ to Lens.

```
GET /activateCluster
  ?cloudUrl={string}
  &namespace={string}
  &clusterName={string}
  &clusterId={string}
```

- `cloudUrl`: URL to the instance, e.g. `https://container-cloud.my-company.com`
- `namespace`: ID of the Container Cloud namespace containing the cluster to activate.
- `clusterName`: Name of the cluster to activate.
- `clusterId`: ID of the cluster (in `namespace`) to activate.

#### Add one cluster

Adds a __single__ cluster to Lens (if it hasn't already been added) by providing a pre-configured kubeConfig JSON object for the cluster. As such, this endpoint does not require the extension to perform any authentication/authorization requests. It simply stores the kubeConfig on disk and tells Lens where to find it.

```
GET /kubeConfig
  ?cloudUrl={string}
  &namespace={string}
  &clusterName={string}
  &clusterId={string}
  &kubeConfig={string}
```

- `cloudUrl`: URL to the instance, e.g. `https://container-cloud.my-company.com`
- `namespace`: ID of the Container Cloud namespace containing the cluster to activate.
- `clusterName`: Name of the cluster to activate.
- `clusterId`: ID of the cluster (in `namespace`) to activate.
- `kubeConfig`: JSON-stringified, Base64-encoded kubeConfig payload.

#### Add multiple clusters

Allows the user to add __one or more__ clusters to Lens by telling the extension where to find them. Unlike [adding one cluster](#add-one-cluster), it does not automatically add any clusters to Lens. It simply triggers the extension to immediately list all available clusters, and then lets the user choose which ones to add.

```
GET /addClusters
  ?cloudUrl={string}
  &username={string}
  &tokens={string}
  [ &keycloakLogin={boolean} ]
  [ &namespaces={string} ]
```

- `cloudUrl`: URL to the instance, e.g. `https://container-cloud.my-company.com`
- `username`: Username associated with the `tokens`.
- `tokens`: JSON-stringified, Base64-encoded OAuth2 tokens for the user.
- `keycloakLogin` (Optional): `false` (default) if the instance in `cloudUrl` uses basic (username/password) authentication; `true` if the instance in `cloudUrl` uses SSO authorization.
- `namespaces` (Optional): Comma-delimited list of namespace IDs to restrict the list of clusters presented by the extension (i.e. a filter on namespaces). Only clusters in these namespaces will be listed.