Use properties.

[dblock]

Description

From #28 (review).

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[codecov]

Codecov Report

Merging #29 (7e29371) into main (b92e9f5) will increase coverage by 0.23%.
Report is 1 commits behind head on main.
The diff coverage is 95.12%.

@@            Coverage Diff             @@
##             main      #29      +/-   ##
==========================================
+ Coverage   93.44%   93.68%   +0.23%     
==========================================
  Files          43       47       +4     
  Lines        1205     1282      +77     
==========================================
+ Hits         1126     1201      +75     
- Misses         79       81       +2     

Files Changed	Coverage Δ
...xtensions_restexecuteonextensiontaction_handler.py	72.22% <33.33%> (ø)
...c/opensearch_sdk_py/rest/extension_rest_handler.py	81.81% <81.81%> (ø)
...s/internal/discovery_extensions_request_handler.py	72.22% <100.00%> (+1.63%)	⬆️
.../opensearch_sdk_py/rest/extension_rest_handlers.py	100.00% <100.00%> (ø)
.../opensearch_sdk_py/rest/extension_rest_response.py	100.00% <100.00%> (ø)
src/opensearch_sdk_py/rest/named_route.py	100.00% <100.00%> (ø)
...earch_sdk_py/transport/outbound_message_request.py	100.00% <100.00%> (ø)

[dbwiddis]

Should we also use properties for routes here and here?

[dblock]

Should we also use properties for routes here and here?

Yep, done.