update online repo configurator for rolling releases

All releases below 11.3 and all LTS releases are shown as before.
All non-LTS releases starting from 11.3 are not shown, instead there is one entry that looks like

• 11.x Rolling (currently 11.3)

For example, for 11.6 release the selection should be like

• 11.x Rolling (currently 11.6)
• 11.4
• 11.2
• 11.1
• 10.11
• ... etc

Note that 11.4 is LTS, so it'll have its own line. And after the 11.4.2 release the "rolling" line will also have "currently 11.4"

this issue is blocked by MDEV-34007, meaning, do not do it until the blocking issue is done