fix(promtail): Fix UDP receiver on syslog transport

[joshuapare]

Simple fix to convert the incoming datagram into a bytes reader that the ParseStream can handle. currently it freezes up because the datagrams are sent as is without separation so the reader routine blocks until an interrupt.

Issue first resolved in grafana/agent, mirror PR to that: grafana/agent#5297

Fixes #6772

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• CHANGELOG.md updated

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[cstyan]

@joshuapare looks like there's some test failures + a merge conflict with the changelog. Assigning myself as reviewer.

[cstyan]

@joshuapare we can move forward here, no issues with the promtail maintenance mode bit. Is there any easy openings for tests here? I'm not very familiar with syslog so I don't know why the reading from the wire needs to be read in this manner to handle UDP.

[joshuapare]

@cstyan Unfortunately not - in the other repo, it was deemed simple enough to merge in, so I assume it would follow the same pattern here: grafana/agent#5297 (review)

[cstyan]

@cstyan Unfortunately not - in the other repo, it was deemed simple enough to merge in, so I assume it would follow the same pattern here: grafana/agent#5297 (review)

fair enough, the agent/alloy team would have worked with this part of the code more recently anyways 👍 lets see if CI is still green, then we can merge

[cstyan]

@joshuapare thanks for your patience 👍

[joshuapare]

@cstyan Same to you! I should have checked back far sooner 😅 thanks for getting this in