Updated docs to register actor endpoint via top-level registrations

[WhitWaldo]

Description

With the release of .NET 8, a warning for ASP0014 was added that suggests that routes shouldn't be registered via app.UseEndpoints and longer and should rather be registered directly from the built web application.

This requires no changes to the SDK itself, but the documentation should be updated to reflect the change and this PR corrects this as was pointed out by the issue in #1256.

Issue reference

We strive to have all PR being opened based on an issue, where the problem or feature have been discussed prior to implementation.

Please reference the issue this PR will close: #1256

Checklist

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• Code compiles correctly (not applicable, no code changes made)
• Created/updated tests (not applicable, no code changes made)
• Extended the documentation

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.28%. Comparing base (1b7c9f4) to head (885a641).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1262   +/-   ##
=======================================
  Coverage   67.28%   67.28%           
=======================================
  Files         174      174           
  Lines        6025     6025           
  Branches      671      671           
=======================================
  Hits         4054     4054           
  Misses       1802     1802           
  Partials      169      169           

Flag	Coverage Δ
net6	67.26% <ø> (ø)
net7	67.26% <ø> (ø)
net8	67.27% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.