doc: examples use declarative configuration 1/N

[coryan]

This is the first in a series of PRs to convert all examples to use declarative configuration for the signature type.

Part of the work for #345

[codecov[bot]]

Codecov Report

Merging #356 (9f4d9b6) into main (498a3aa) will increase coverage by 0.08%. The diff coverage is 98.24%.

:exclamation: Current head 9f4d9b6 differs from pull request most recent head 287f17b. Consider uploading reports for the commit 287f17b to get more accurate results

@@            Coverage Diff             @@
##             main     #356      +/-   ##
==========================================
+ Coverage   89.26%   89.35%   +0.08%     
==========================================
  Files          98       98              
  Lines        2739     2761      +22     
==========================================
+ Hits         2445     2467      +22     
  Misses        294      294              

Impacted Files	Coverage Δ
examples/hello_cloud_event/hello_cloud_event.cc	80.00% <80.00%> (+5.00%)	:arrow_up:
examples/cloud_event_examples_test.cc	100.00% <100.00%> (ø)
...mples/hello_from_namespace/hello_from_namespace.cc	100.00% <100.00%> (ø)
...om_nested_namespace/hello_from_nested_namespace.cc	100.00% <100.00%> (ø)
...s/hello_multiple_sources/hello_multiple_sources.cc	100.00% <100.00%> (ø)
...s/hello_with_third_party/hello_with_third_party.cc	100.00% <100.00%> (ø)
examples/hello_world/hello_world.cc	100.00% <100.00%> (ø)
...les/howto_use_legacy_code/howto_use_legacy_code.cc	100.00% <100.00%> (ø)
examples/http_examples_test.cc	100.00% <100.00%> (ø)
... and 1 more

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