Perf: Improving async/await usages

[henriqueholtz]

The changes are made based on .NET AsyncGuidance.

• async/await improvements
• Got rid a lot of synchronous flows
• Included some new unit tests
• Adding a postman collection to easily test the new version (that needs some manual steps for now, and have a lot of things to improve. Maybe soon can be a github action). Additional informations on README
• Fixing a bug when searching something in the home page (is already in the postman collection. Which means run the collection before the merge will fail the request, after the merge all will be passing)

[AppVeyorBot]

:white_check_mark: Build Sharebook-Backend: PR Check 1.0.93-gbnaexlv completed (commit https://github.com/SharebookBR/sharebook-backend/commit/2424ba15f6 by @henriqueholtz)

[AppVeyorBot]

:white_check_mark: Build Sharebook-Backend: PR Check 1.0.93-gbfgckxc completed (commit https://github.com/SharebookBR/sharebook-backend/commit/14ed57baca by @henriqueholtz)

[AppVeyorBot]

:white_check_mark: Build Sharebook-Backend: PR Check 1.0.93-mocsinxm completed (commit https://github.com/SharebookBR/sharebook-backend/commit/2b0dce87b2 by @henriqueholtz)

[AppVeyorBot]

:white_check_mark: Build Sharebook-Backend: PR Check 1.0.93-xnpeqfkm completed (commit https://github.com/SharebookBR/sharebook-backend/commit/f7f698edc5 by @henriqueholtz)

[sonarcloud[bot]]

Quality Gate failed

Failed conditions
10.5% Coverage on New Code (required ≥ 80%)

See analysis details on SonarCloud

[AppVeyorBot]

:white_check_mark: Build Sharebook-Backend: PR Check 1.0.93-uohquwfr completed (commit https://github.com/SharebookBR/sharebook-backend/commit/96bcff3c27 by @henriqueholtz)