Put back support to produce in the old DecatonTaskRequest for migration

[kawamuray]

Related to: https://github.com/line/decaton/pull/238/files

In https://github.com/line/decaton/pull/238/files and https://github.com/line/decaton/pull/238/files we dropped the DecatonTaskRequest w/ online migration procedure.

However, in the apps that uses both decaton-processor and decaton-client (i.e, DecatonClient), it is impossible to migrate the app to decaton 9 or above because it inherently upgrades decaton-client dep by transitive dep from decaton-processor first.
To address this situation I put back the option to let DecatonClient keep producing tasks in older version until all processor completes upgrade.

After this change the upgrade procedure will be:

• Step1: Upgrade decaton-processors to 9.0.0 or higher with decaton.retry.task.in.legacy.format=true, decaton.legacy.parse.fallback.enabled=true. Also set produceInOldTaskRequest to true in DecatonClientBuilder if you're using the DecatonClient in the same app.
• Step2: Upgrade decaton-clients to 9.0.0 or higher
• Step3: After all decaton-processors are upgraded, set decaton.retry.task.in.legacy.format=false, Also set produceInOldTaskRequest to false in DecatonClientBuilder if you're using the DecatonClient in the same app.
• Step4: Wait all old-format tasks and retry tasks are processed after Step3.
  • You can monitor topic's committed offset is caught-up and retry-topic's offset lag becomes 0.
• Step5: Set decaton.legacy.parse.fallback.enabled=false

[ocadaruma]

it inherently upgrades decaton-client dep by transitive dep from decaton-processor first

Nice catch. I overlooked this point.

LGTM