fix: faster update of file tasks for loki.source.file

[kalleep]

PR Description

loki.source.file have a main loop that is responsible to read and forward log entries from tailer tasks. When we get an update to add new tasks we store new tasks and add a signal to this main loop, this is done to keep calls to Update cheap.

The problem is that we will not update running tasks if we are blocked on sending an entry. This pr splits up the consumer work and task scheduling into two different go routines. With this change we no longer need to start a drain job while we update tasks.

Which issue(s) this PR fixes

Notes to the Reviewer

PR Checklist

• CHANGELOG.md updated
• Documentation added
• Tests updated
• Config converters updated

[Copilot]

Pull Request Overview

This PR optimizes the loki.source.file component by splitting the main loop into two separate goroutines: one for consuming and forwarding log entries, and another for managing task updates. This architectural change eliminates blocking issues where task updates were delayed when the system was busy sending entries, removing the need for a drain job during updates.

Key changes:

• Separated log entry consumption and task scheduling into independent goroutines using a WaitGroup
• Removed the complex drain goroutine mechanism that was previously needed during task updates
• Enhanced local.file_match component with immediate update triggers and change detection to reduce unnecessary exports

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
internal/component/loki/source/file/file.go	Refactored main loop into two goroutines (consumer and scheduler), removed drain mechanism, improved error handling for task updates
internal/component/local/file_match/file.go	Added trigger channel for immediate updates, implemented target comparison to avoid redundant exports, changed RWMutex to Mutex