Fix treasury kept and spend when emptied

[gui1117]

Fix #3879
Superseed #3797

Done:

• treasury account is created at genesis config.
• pot doesn't include existential deposit thus pot can be entirely spend with no issue.

TODO:

• update polkadot: just includes Config in construct_runtime
• fix some tests using runtime genesis config

Alternatives:

• we could also keep old behavior with treasury being created when it happens that dilution is more than ED. but seem better that we create it once and for all.

Notes:

• I still kept resolve_creating to ensure it still works on Kusama if there is no treasury account then it will just get created once on_dilution mint more than ED instead of never be created.
  Also in case someone forget to include Config in construct runtime (thus account is not created) then this account can be created later as well.

[kianenigma]

Now that we have better runtime logging I do get tempted to do something like resolve_exisiting().unwrap_or_else(|_| { log("CODE RED, SOS"); resolve_creating() ).

But I assume it depends on the proof. If it is logically impossible to cause account creation then this is also good.

[gui1117]

interesting indeed a lot of such safe operation could be logged 🤔

[kianenigma]

PR looks good already;
Maybe we can add a test case to make sure:

• Real pot (before subtracting ed) is always above ed even if more is requested to spend
• Integration test fo the proper creation of treasury account similar to what will happen in KSM

[gui1117]

I would very suspect that treasury does exist already in kusama, but anyway it is fine. and I added both tests.

another solution would be to lazily create the account if it happens that it doesn't exist but whatever is OK

[gui1117]

test are failing at least because of some CI issue, let's retry them

[kianenigma]

Could use the suggestion for test otherwise LGTM and ready to merge.