manager: error_stream_name validation.

Flink job naming conventions in Event Platform (k8s deployment-chart) break some assumptions that were made for error sink name auto generation.

Flink job names can contain hyphens, which is an invalid character for stream names. As a result error_sink must always be explicitly declared in helmfile configs.

This MR improves error_sink logic by:

• removing the boolean option from the error_sink stream manager parameter. This makes it explicit that error_sink must always be declared.
• adding validation to check that an error stream name does not contain invalid characters. Stream name validation should not enabled by default on all streams: we might want to consume streams that for historical reasons are now considered "invalid". However we should make sure that the streams generated by eventutilities-python are valid.

Bug: T336488

cc @otto @tchin