[node] fix labels

[BulatSaif]

Fixes #350

If docker tag is more than 64 characters or has Invalid value, deployment will fail.
values:

image:
  repository: parity/polkadot
  tag:latest@sha256:8bc39c8a98eef9d063241ad0f8527ef7922794757edd30da2e3308f720bd1b61

Error:

Error: UPGRADE FAILED: cannot patch "bootnode" with kind ServiceAccount: ServiceAccount "bootnode" is invalid: [metadata.labels: Invalid value: "latest@sha256:8bc39c8a98eef9d063241ad0f8527ef7922794757edd30da2e3308f720bd1b61": must be no more than 63 characters, metadata.labels: Invalid value: "latest@sha256:8bc39c8a98eef9d063241ad0f8527ef7922794757edd30da2e3308f720bd1b61": a valid label must be an empty string or consist of alphanumeric characters, '-', '_' or '.', and must start and end with an alphanumeric character (e.g. 'MyValue',  or 'my_value',  or '12345', regex used for validation is '(([A-Za-z0-9][-A-Za-z0-9_.]*)?[A-Za-z0-9])?')]