Improve documentation of destination_conf parameter

[victor-perov]

Summary

This commit sheds more light on destination_conf attribute of logpush job configuration by adding details on the format it has and stresses more details on accepted schemes such as r2, sumo, etc.

Documentation checklist

• [ ] The documentation style guide has been adhered to.
• [x] If a larger change - such as adding a new page- an issue has been opened in relation to any incorrect or out of date information that this PR fixes.
• [ ] Files which have changed name or location have been allocated redirects.

[victor-perov]

@soheiokamoto @angelampcosta please review when you get a chance. This change was motivated by a set of customer support tickets.

[victor-perov]

i will ignore those two ai suggestions on this occasion.