Set the backlog metrics interval through the generic override

[delthas]

backbeat.backlogMetricsIntervalSeconds is a dedicated CR field the operator no longer has: scality/zenko-operator#626 added it, scality/zenko-operator#633 reverted it right after v1.8.16 in favour of the generic backbeat.configurationOverrides map.

The two spellings never coexist in a released operator:

operator	backlogMetricsIntervalSeconds	backbeat.configurationOverrides
v1.8.16	works	absent — the field exists only on ZenkoSpecSorbet
v1.8.17	removed	works

So the config and the operator pin have to move together, and bumping the operator without this change fails the whole suite on a rejected field. Hence both in one commit.

The override also needs a backbeat that can take it. The map arrives as environment variables, and 9.5 answers most of those names from an entrypoint that rewrites conf/config.json in place — a directory the operator mounts read-only, so the container dies before it serves anything. KAFKA_BACKLOG_METRICS_INTERVALS is one of the 57 names rewritten that way, which is what failed this branch eight runs in a row. 9.6 deleted the entrypoint and reads those names from the configuration schema itself (BB-808), so the bump to 9.6.0-preview.1 comes first here. That the operator passes these to a backbeat that cannot take them is ZKOP-605.

KAFKA_BACKLOG_METRICS_INTERVALS is backbeat's declared env alias for kafka.backlogMetrics.intervalS (intervalS: joi.number().default(60).meta({ env: 'INTERVALS' })), so the value reaches the same key with the same unit — seconds — as the removed field did, with joi coercing "5" to the number the schema declares. It is set on the four consumers whose lag the lifecycle conductor waits on.

pin	before	after
backbeat	9.5.1	9.6.0-preview.1
zenko-operator	v1.8.16	v1.8.17

Split out of #2532, which carries the same change but is blocked on a zenko-operator 1.9 PR and so cannot land on this timeline.

Issue: ZENKO-5359

[bert-e]

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[delthas]

/approve

[delthas]

!done 5h

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[delthas]

Replaced by #2546

[delthas]

ZENKO-5359: logged 5h; transitioned to Done (Fixed)