…r nix-build

Note that even though `/.*` was ignored, the `.env.example` is still in
the filtered source. This is because `nix-gitignore` appears to prepend
the additional ignores, and thus `!.env.example` in `.gitignore`
overrides the `/.*`.

…TRY`, `CONTAINER_REPOSITORY`, and `REGISTRY_AUTH_FILE`

…d using environment scopes for deployment jobs

…mediate artifacts in `$TMPDIR` instead of hardcoded to `/var/tmp`

… stages of the pipeline

* `integration:deployment` - deploys to testenet
* `integration:prerelease` - deploys to GitLab container registry as `testnet`
* `release:deployment:branch` - deploys to mainnet
* `release:deployment:tag` - deploys to mainnet
* `release:distribution` - deploys to GitLab container registry as `mainnet`

mainnet deployment is still a stub