Add migrationLogLevel configuration

[madsodgaard]

Adds the possibility to configure the log level for migrations with:

app.fluent.migrationLogLeveL = .debug

[codecov-commenter]

Codecov Report

Merging #756 (fd29807) into main (44155a5) will decrease coverage by 0.20%. The diff coverage is 50.00%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #756 +/- ## ========================================== - Coverage 61.02% 60.82% -0.20% ========================================== Files 15 15 Lines 526 531 +5 ========================================== + Hits 321 323 +2 - Misses 205 208 +3 ``` | Flag | Coverage Δ | | |---|---|---| | unittests | `60.82% <50.00%> (-0.20%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#carryforward-flags-in-the-pull-request-comment) to find out more. | [Impacted Files](https://codecov.io/gh/vapor/fluent/pull/756?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor) | Coverage Δ | | |---|---|---| | [Sources/Fluent/FluentProvider.swift](https://codecov.io/gh/vapor/fluent/pull/756?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9GbHVlbnQvRmx1ZW50UHJvdmlkZXIuc3dpZnQ=) | `79.27% <50.00%> (-1.86%)` | :arrow_down: |

[VaporBot]

These changes are now available in 4.7.0