[BUG] "Split lines failed: bufio.Scanner: token too long" for phase with a lot of output

[muffl0n]

Describe the bug
One of our phases increased its output by a huge amount of lines from one day to another.
From 450 lines (40Kb) to 2530 lines (169Kb). This caused Kanister to fail the actionset with the error

Split lines failed: bufio.Scanner: token too long

https://github.com/kanisterio/kanister/blame/master/pkg/output/stream.go#L50

To Reproduce
Steps to reproduce the behavior:

1. Create blueprint
2. Add phase that produces a lot of output: more than 64Kb
3. Run actionset
4. See error

Expected behavior
Output is parsed.

Screenshots
n/a

Environment
Kubernetes Version/Provider: v1.27.7-gke.1121001
Storage Provider: n/a
Cluster Size (#nodes): n/a
Data Size: n/a
Kanister: 0.99.0

Additional context
The default buffer of bufio is 64Kb: https://pkg.go.dev/bufio#pkg-constants
That explains, why the error occurs when crossing this boundary.

const (
	// MaxScanTokenSize is the maximum size used to buffer a token
	// unless the user provides an explicit buffer with Scanner.Buffer.
	// The actual maximum token size may be smaller as the buffer
	// may need to include, for instance, a newline.
	MaxScanTokenSize = 64 * 1024
)

I'm not quite sure how to handle this. Just increasing the buffer blindly to some higher value does not seem like a good solution.

Thread in Slack: https://kanisterio.slack.com/archives/C85C8V22J/p1705490134135299

[github-actions]

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[hairyhum]

@muffl0n thanks for the contribution!

I think it should be addressable by replacing bufio.Scanner. with bufio.Readerand usingReadString`, so should be an easy fix.