Support ExpressOptions.expressInstance in createApp

[LoicPoullain]

Issue

In some situations, we may need to specify both an expressInstance and postMiddlewares to createApp (for example if we're migrating an application from Express to Foal). This is currently not possible to do it properly.

Solution and steps

• Support ExpressOptions.expressInstance in createApp.

Checklist

• Add/update/check docs (code comments and docs/ folder).
• Add/update/check tests.
• Update/check the cli generators.

Related issue

See this discussion: #370

[codecov]

Codecov Report

Merging #547 into v1-2-0 will increase coverage by 0.07%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           v1-2-0     #547      +/-   ##
==========================================
+ Coverage   99.49%   99.57%   +0.07%     
==========================================
  Files          88       88              
  Lines        1586     1636      +50     
  Branches      340      371      +31     
==========================================
+ Hits         1578     1629      +51     
+ Misses          8        7       -1

Impacted Files	Coverage Δ
packages/core/src/express/create-app.ts	98.85% <100%> (+1.41%)	⬆️
packages/core/src/common/utils/controller.util.ts	100% <0%> (ø)	⬆️
...ages/core/src/common/utils/verify-password.util.ts	100% <0%> (ø)	⬆️
packages/core/src/sessions/token-optional.hook.ts	100% <0%> (ø)	⬆️
packages/core/src/sessions/token-required.hook.ts	100% <0%> (ø)	⬆️
packages/core/src/sessions/set-session-cookie.ts	100% <0%> (ø)	⬆️
...api/metadata-getters/get-api-complete-operation.ts	100% <0%> (ø)	⬆️
packages/core/src/express/create-middleware.ts	100% <0%> (ø)	⬆️
packages/core/src/express/handle-errors.ts	100% <0%> (ø)	⬆️
...ackages/core/src/sessions/remove-session-cookie.ts	100% <0%> (ø)	⬆️
... and 7 more

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