feat: refactor credentials fetching

[alnr]

This change revamps the way we fetch identity credentials. We no longer need most of the helper fields for gobuffalo/pop inside the Identity and Credentials structures, and we collect all the credentials in one joined query rather than using pop's EagerPreload functionality.

[aeneasr]

Very nice changes, I think this simplifies the code a lot!

[aeneasr]

It looks like you're running into ordering issues: https://github.com/ory/kratos/actions/runs/4492557398/jobs/7902651309?pr=3183#step:15:12872

Every database handles "deafult" sorting differently. Since we don't really want to sort the dataset (as that is slow in RBR tables), my recommendation is to either sort the result set (with Go) around here: https://github.com/ory/kratos/pull/3183/files#diff-41d54e67508bfcb98af6522993d007de47a74ada2cf8426fc871c8a8a8babaeeR561

[codecov]

Codecov Report

Merging #3183 (9999e7f) into master (a206772) will increase coverage by 0.02%.
The diff coverage is 86.18%.

❗ Current head 9999e7f differs from pull request most recent head 0dad8c2. Consider uploading reports for the commit 0dad8c2 to get more accurate results

@@            Coverage Diff             @@
##           master    #3183      +/-   ##
==========================================
+ Coverage   77.62%   77.65%   +0.02%     
==========================================
  Files         317      317              
  Lines       20046    20089      +43     
==========================================
+ Hits        15561    15600      +39     
- Misses       3292     3295       +3     
- Partials     1193     1194       +1     

Impacted Files	Coverage Δ
driver/registry_default.go	86.92% <ø> (ø)
identity/credentials.go	77.77% <ø> (-2.23%)	⬇️
identity/identity.go	91.30% <ø> (+3.24%)	⬆️
identity/identity_verification.go	70.96% <ø> (ø)
identity/test/pool.go	100.00% <ø> (ø)
selfservice/flow/verification/flow.go	92.00% <ø> (ø)
selfservice/flow/settings/flow.go	91.54% <60.00%> (ø)
selfservice/hook/verification.go	72.41% <60.00%> (ø)
persistence/sql/identity/persister_identity.go	78.32% <85.55%> (+1.68%)	⬆️
selfservice/strategy/code/strategy_verification.go	75.49% <86.20%> (ø)
... and 7 more

... and 1 file with indirect coverage changes

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[aeneasr]

Generally speaking i think this looks really good. One issue though is how we now list identities. We had several complains from e.g. Wikia about list performance before and we were able to resolve those with EagerPreload. This patch will regress on those improvements and reintroduce those issues. See: #1412

[aeneasr]

Very nice