Record server startup time in ProfileEvents

[SmitaRKulkarni]

Changelog category (leave one):

• Feature

Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):
Record server startup time in ProfileEvents resolves #43188
Implementation:

• Added ProfileEvents::ServerStartupMilliseconds.
• Recorded time from start of main till listening to sockets.
  Testing:
• Added a test 02532_profileevents_server_startup_time.sql

[qoega]

Do you know if internal port is up before we accept external http/native connections? I had an integration test(#45156) where it was important to check it is up.
Don't you think it will be useful to add Events per interface as a follow up?

[alexey-milovidov]

It's ok to have a single event for the time when all the listeners are up.

[qoega]

Still, do we guarantee that all listeners are up when we write those? What is the order of endpoint initialization? How can you check that all are ready - just OK on http or native will not work and query event is inadequate.

[alexey-milovidov]

They are initialized in a sequence and are ready at similar times (except the embedded Keeper, but it does not matter). It's ok if the metric overestimates the startup time a little. Therefore, let's record the time after starting the last of the listeners.