fix(datadog_logs sink): abort serialization and split batch when payload is too large (#19189)

* add failing test

Signed-off-by: Luke Steensen <luke.steensen@gmail.com>

* abort and split batch serialization when too large

Signed-off-by: Luke Steensen <luke.steensen@gmail.com>

* clippy

Signed-off-by: Luke Steensen <luke.steensen@gmail.com>

* Update src/sinks/datadog/logs/sink.rs

Co-authored-by: Doug Smith <dsmith3197@users.noreply.github.com>

* do not double count byte size when splitting

Signed-off-by: Luke Steensen <luke.steensen@gmail.com>

* emit dropped event

Signed-off-by: Luke Steensen <luke.steensen@gmail.com>

* add changelog entry

Signed-off-by: Luke Steensen <luke.steensen@gmail.com>

* Update changelog.d/OPW-86.fix.md

Co-authored-by: neuronull <neuronull@pm.me>

* rename changelog fragment

Signed-off-by: Luke Steensen <luke.steensen@gmail.com>

* use dougs idea

Signed-off-by: Luke Steensen <luke.steensen@gmail.com>

* remove unnecessary clone

Signed-off-by: Luke Steensen <luke.steensen@gmail.com>

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Signed-off-by: Luke Steensen <luke.steensen@gmail.com>
Co-authored-by: Doug Smith <dsmith3197@users.noreply.github.com>
Co-authored-by: neuronull <neuronull@pm.me>