Prometheus exporters

This is based on !71 (merged) and thus needs to be merged before merging this MR.

added 4 commits

• 8b3c68e5 - 1 commit from branch master
• 118a9da4 - Introduce prometheus exporters role for collection
• 284837aa - Add blackbox exporter for https status checking
• e9b4d9ff - Add rebuilderd build queue length textcollector

Compare with previous version

added 4 commits

• ca5a3ffd - 1 commit from branch master
• 6cfba72a - Introduce prometheus exporters role for collection
• c111e439 - Add blackbox exporter for https status checking
• 6639ae76 - Add rebuilderd build queue length textcollector

Compare with previous version

added 3 commits

• c82151e2 - Introduce prometheus exporters role for collection
• 1064e433 - Add blackbox exporter for https status checking
• f39a9949 - Add rebuilderd build queue length textcollector

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approved this merge request

added 4 commits

• ca5a3ffd - 1 commit from branch master
• 02aa1507 - Introduce prometheus exporters role for collection
• 0a796d30 - Add blackbox exporter for https status checking
• 9c972f58 - Add rebuilderd build queue length textcollector

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resolved all threads

seems superseded by !73 (merged) at least thats where i wrote all my feedback

added 28 commits

• 9c972f58...d16d80fb - 25 commits from branch master
• f28cac70 - Introduce prometheus exporters role for collection
• fad61c53 - Add blackbox exporter for https status checking
• e4128d84 - Add rebuilderd build queue length textcollector

Compare with previous version

added 3 commits

• 23564b29 - Introduce prometheus exporters role for collection
• 3fd36ddb - Add blackbox exporter for https status checking
• cd4b2844 - Add rebuilderd build queue length textcollector

Compare with previous version

merged

mentioned in commit ff9358a9