Results CLI: List and Get Events for PipelineRuns and TaskRuns

[adambkaplan]

Feature request

Add the following event-related subcommands to tkn results:

• pipelinerun events list: list events for a provided PipelineRun
• pipelinerun events get: get a specific event (by ID)
• taskrun events list: list events for a provided TaskRun
• taskrun events get: get a specific event (by ID)
• events list: list events (all for a given namespace)
• events get: get a specific event (by ID)

Use case

Query and analyze events that occur during the execution of a TaskRun and/or PipelineRun.

See also #439

[khrm]

@divyansh42 We can include this in feature list.