CI: Add pre-release test stage

[Syndesi]

Add a pre-release test stage to the CI, which:

• Executes the regular test CI
• Executes advanced compatibility tests, see Alternative graph databases #286 , Alternative search database #289 , Alternative queue databases #291 , Alternative document database #287 , Alternative key-value database #288 , Alternative S3 compatible storage #290 etc.
• Executes time-limit related tests against the server's actual configuration, not just against slower (but still real) time limits