fix: update StartK8sStreamWithHeartBeat to use context for cancellation and improve error handling

[Ash-exp]

Description

Fixes https://github.com/devtron-labs/sprint-tasks/issues/2885

Checklist:

• The title of the PR states what changed and the related issues number (used for the release note).
• Does this PR requires documentation updates?
• I've updated documentation as required by this PR.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have tested it for all user roles.
• I have added all the required unit/api test cases.

Does this PR introduce a user-facing change?

Summary by Bito

• Added context.Context parameter to StartK8sStreamWithHeartBeat method in Pump interface and implementation for cancellation support.
• Replaced regexp usage with strings.SplitN for log parsing and added handling for blank or malformed log lines to continue instead of aborting.
• Improved goroutine management with context cancellation checks and changed done channel to chan struct{} for efficiency.
• Added conditional flushing in heartbeat and main loop to avoid unnecessary operations on errors.
• Updated the caller in k8sApplicationRestHandler.go to pass context and removed redundant stream close defer.

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud