Add finally tasks to Tekton pipelines

What this post added

Introduces the `finally` clause in Tekton Pipelines (v0.14.0) for executing tasks after pipeline completion, regardless of success or failure. Details use cases such as sending notifications and cleaning up resources. Explains how `finally` tasks affect the overall `pipelineRun` status. Introduces features for conditional execution of `finally` tasks using `when` expressions and accessing task execution status (`$(tasks.<task-name>.status)`, `$(tasks.status)`). Describes how to pass task results to `finally` tasks (`$(tasks.acquire.results.leased-resource)`). Details graceful termination of pipeline runs with `CancelledRunFinally` and `StoppedRunFinally` statuses.