Fix HotROD instructions

[yurishkuro]

Which problem is this PR solving?

• The README was showing a command with the legacy OTEL_EXPORTER_JAEGER_ENDPOINT env var (using Jaeger format)

Description of the changes

• Change to use OTEL_EXPORTER_OTLP_ENDPOINT to match the docker-compose setup.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.10%. Comparing base (ccecb7f) to head (402bec7).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5273      +/-   ##
==========================================
+ Coverage   95.09%   95.10%   +0.01%     
==========================================
  Files         339      339              
  Lines       16511    16511              
==========================================
+ Hits        15701    15703       +2     
+ Misses        621      620       -1     
+ Partials      189      188       -1     

Flag	Coverage Δ
cassandra-3.x	26.53% <ø> (ø)
cassandra-4.x	26.53% <ø> (ø)
elasticsearch-5.x	21.77% <ø> (ø)
elasticsearch-6.x	21.77% <ø> (+0.01%)	⬆️
elasticsearch-7.x	21.85% <ø> (ø)
elasticsearch-8.x	21.92% <ø> (-0.02%)	⬇️
grpc-badger	19.23% <ø> (ø)
kafka	14.66% <ø> (ø)
opensearch-1.x	21.84% <ø> (ø)
opensearch-2.x	21.84% <ø> (-0.02%)	⬇️
unittests	92.72% <ø> (+0.01%)	⬆️

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.