[Actors API] update err desc to be more explicit

[cicoyle]

Ran into some errors with using the Actors API & reminders. This PR is a nice to have making it explicit to newbie actor users what the error means.

This PR fixes one of the issues, which I also had locally and confirm resolves the err:

== APP == 2024/10/22 13:54:53 http: superfluous response.WriteHeader call from [github.com/dapr/go-sdk/service/http.(*Server).registerBaseHandler.func6](http://github.com/dapr/go-sdk/service/http.(*Server).registerBaseHandler.func6) (topic.go:214)

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 55.79%. Comparing base (6c59092) to head (d1d687c).
⚠️ Report is 37 commits behind head on main.

Files with missing lines	Patch %	Lines
actor/manager/manager.go	0.00%	1 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (6c59092) and HEAD (d1d687c). Click for more details.

HEAD has 3 uploads less than BASE

Flag	BASE (6c59092)	HEAD (d1d687c)
	4	1

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #643      +/-   ##
==========================================
- Coverage   62.52%   55.79%   -6.74%     
==========================================
  Files          56       58       +2     
  Lines        4139     3692     -447     
==========================================
- Hits         2588     2060     -528     
- Misses       1425     1496      +71     
- Partials      126      136      +10     

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

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[mikeee]

lgtm

[cicoyle]

I am simply changing the text in the errors.New() but nothing else, can this be merged even with the codecov failure since Im just trying to make the error make sense to users when they see it bc as-is, it makes no sense.