Support out-of-cluster installation

[salasberryfin]

What this PR does / why we need it:

This is intended to allow a Rancher operator to choose between deploying rancher-turtles in the same or a different cluster to Rancher Manager. The current implementation of rancher-turtles defaults to an in-cluster configuration with both Rancher Manager and rancher-turtles supposed to be installed together in the same cluster.

The initial idea is to create the client based on whether a flag with a path to a kubeconfig file is passed. When this parameter is used, rancher-turtles will load the REST Config from this file and create a client for an out-of-cluster installation. If it is not, it defaults to the current in-cluster behavior.

Issue #19

Special notes for your reviewer:

Checklist:

• squashed commits into logical changes
• includes documentation
• adds unit tests
• adds or updates e2e tests

[furkatgofurov7]

While this is clear to the internal team, it would be nice to have a small document describing what is (out-of/in)-cluster support, the difference between them and why it is needed.

Please disregard if we have a separate issue to document it in rancher-turtles-docs

[Danil-Grigorev]

Same thought as @furkatgofurov7, but additionally we need to have some clear process to pass the kubeconfig to the pod, which could be documented in rancher-turtles-docs + not necessary in the same PR but would prefer to have e2e test coverage here to be sure.

[richardcase]

@furkatgofurov7 @Danil-Grigorev @salasberryfin - i created #94 for us to create an ADR for this.

[furkatgofurov7]

@furkatgofurov7 @Danil-Grigorev @salasberryfin - i created #94 for us to create an ADR for this.

Except this, I have nothing major to not merge it

[salasberryfin]

Thanks for the reviews @richardcase @Danil-Grigorev @furkatgofurov7. I'll be taking on the ADR proposal to have this well documented.

[salasberryfin]

I addressed the latest comments and created a PR for the ADR #95.

[richardcase]

This looks good to me, thanks @salasberryfin

We will need to create a documentation issue (in racher-turtles-docs) to cover:

• Handling the RBAC, service account etc
• How to create the secret and mount it

[salasberryfin]

I created rancher/turtles-docs#13 to track this.

[furkatgofurov7]

@salasberryfin can we rebase it?

[salasberryfin]

The changes are now up to date after rebase, please take a look.

[furkatgofurov7]

Thanks @salasberryfin!