[chore][testbed] add filelog as a part of test cases

[VihasMakwana]

Recently, we added memory limiter test cases for OTLP.
This PR updates the cases to work with filelog sender as well.

[VihasMakwana]

@ChrsMark can you please take at this PR? I've used options.

[ChrsMark]

Overall LGTM.

[ChrsMark]

Out of curiosity, is this change required for the test that this PR adds? From what I can see it should be fine to include it but just want to understand why.

[VihasMakwana]

Yeah. It's required.

filelogwriter accepts logs in plog.Log and writes them in file. Here

opentelemetry-collector-contrib/testbed/datasenders/stanza.go

Lines 68 to 72 in 9cb09d5

	for k := 0; k < ills.LogRecords().Len(); k++ {
	_, err := f.file.Write(append(f.convertLogToTextLine(ills.LogRecords().At(k)), '\n'))
	if err != nil {
	return err
	}

This is kind of a special case where the log attributes are a part of log body itself. That why I use regex.

For other senders (such as otlp), we start the corresponding exporter for a sender. In such scenarios, the attributes are preserved.

Let me know if you have any questions.