[all] make otel sync gauge emit last recorded metrics in every export interval

[m-nagarajan]

Problem Statement

In AggregationTemporalitySelector#deltaPreferred() : GAUGE falls back to default i,e DELTA, which results in no data getting exported if a synchronousGAUGE instrument is not recorded in that export interval, resulting in patches of data only whenever the metric is recorded.

Solution

Raised an issue with OSS OTel open-telemetry/opentelemetry-java#7634 and it was concluded that its intentionally kept that way by design as an instrument should not emit old recorded data unless its recorded in that export interval.
This PR makes GAUGE to be CUMULATIVE based on the below config which is enabled by default.
otel.venice.export.last.recorded.value.for.synchronous.gauge

Code changes

• Added new code behind a config. If so list the config names and their default values in the PR description.
• Introduced new log lines.
  • Confirmed if logs need to be rate limited to avoid excessive logging.

Concurrency-Specific Checks

Both reviewer and PR author to verify

• Code has no race conditions or thread safety issues.
• Proper synchronization mechanisms (e.g., synchronized, RWLock) are used where needed.
• No blocking calls inside critical sections that could lead to deadlocks or performance degradation.
• Verified thread-safe collections are used (e.g., ConcurrentHashMap, CopyOnWriteArrayList).
• Validated proper exception handling in multi-threaded code to avoid silent thread termination.

How was this PR tested?

• New unit tests added.
• New integration tests added.
• Modified or extended existing tests.
• Verified backward compatibility (if applicable).

Does this PR introduce any user-facing or breaking changes?

• No. You can skip the rest of this section.
• Yes. Clearly explain the behavior change and its impact.
  Otel Sync Gauge metrics will always export the last recorded value unless this config is disabled.