Add config for the buffer

[TheJokersThief]

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The Pull Request

What is the reason for this change

The cleanup script adds a hardcoded buffer time of 30 minutes to its decision making. This is fine if you're working on the scale of days (the default scale is 24hours) but we've found a want to kill pending jobs a lot sooner (on the scale of 20-30 mins) to avoid large backlogs of builds and a thundering herd problem as they start running.

This PR proposes to keep the default behaviour, but make the buffer configurable so that folks can tune it to their needs :)

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[eoinmcafee00]

Hi @TheJokersThief

Thank you for submitting this PR. While the intention is to "keep the default behavior and make the buffer configurable to accommodate various needs," it appears that a default buffer of 30 minutes has been set. This change would impact everyone, which may not be ideal.

[TheJokersThief]

@eoinmcafee00 The 30 min default will stay the same 😄 https://github.com/harness/drone/pull/3308/files#diff-ec2dbfc0f3608fdb5f84d2410a35bb3a90a147535ae41dbc10d0f190f5eebbd6R61

[eoinmcafee00]

ah I missed the last line @TheJokersThief