feat: new "immediate" trigger mode for decision log plugin

[sspaink]

Why the changes in this PR are needed?

resolve: #7455

What are the changes in this PR?

This introduced a new trigger mode:

decision_logs.reporting.trigger=immediate

This trigger mode will upload events either if the upload size limit is reached or after the maximum delay.

Using this trigger mode disables configuring the decision_logs.reporting.min_delay_seconds and only the decision_logs.reporting.max_delay_seconds can be changed.

Notes to assist PR review:

The(p *Plugin) loop()method can now spin up a separate routine when using this new trigger mode that waits for a message from a buffer. Both the size and event buffer use the chunkEncoder which returns a result when a chunk is ready. The difference is that the size buffer adds the event to the encoder on log while the event buffer adds the event to the encoder on upload.

For the size buffer to support this mode I added a new channel (immediateResult) to notify there is a chunk ready. While the event buffer already uses a buffered channel it behaves the same reading from it until a chunk is ready.

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