Value of `.dockerconfigjson` in kubernetes_secret datasource is already
decoded, so I encode it again to avoid error for
`ENVBUILDER_DOCKER_CONFIG_BASE64`
This PR changes template names and docs to follow the
`<provider>-<os/whatever>` format for all templates.
I've decided not to split this into multiple PRs because I'd have to
edit rebase the other PRs once one of them gets merged, this should be
relatively low-impact anyways.
This aligns with our goals to make templates more user-friendly.
Closes#15754
Eric Paulsen