Delay logging config warnings until the logger has been initialized

[yvrhdn]

What this PR does:
While adding config warnings in #2543 I noticed the warnings never got printed. Because we print the warnings while loading the configuration, we log them using the default NoopLogger...

This PR holds on to the warnings until we initialized the logger and can correctly log them.

End result:

level=warn ts=2023-07-12T16:30:04.59588Z caller=main.go:78 msg="-- CONFIGURATION WARNINGS --"
level=warn ts=2023-07-12T16:30:04.595906Z caller=main.go:78 msg="c.Distributor.LogReceivedTraces is deprecated. The new flag is c.Distributor.log_received_spans.enabled"
level=warn ts=2023-07-12T16:30:04.595911Z caller=main.go:78 msg="Trace storage conflict with user-configuirable overrides storage"
level=info ts=2023-07-12T16:30:04.595916Z caller=main.go:222 msg="initialising OpenTracing tracer"
...

Which issue(s) this PR fixes:
Fixes #

Checklist

• Tests updated
• Documentation added
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]

[yvrhdn]

Alternative solutions:

• just print warnings to stdout
• do a second pass over the config after we initialized the logger to print warnings

[joe-elliott]

i swear i've seen it correctly print warnings before. /shrug