dynamic_modules: allow user to set the stat prefix for dynamic module stats

[wtzhang23]

Commit Message: allow user to set the stat prefix for dynamic module stats
Additional Description: Provides the ability for the user to specify the string prefix prepended before all metrics created by their module
Risk Level: Low
Testing: Unit + Integration
Docs Changes: N/A
Release Notes: N/A
Platform Specific Features: N/A

[repokitteh-read-only]

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🐱

Caused by: #41215 was opened by wtzhang23.

see: more, trace.

[repokitteh-read-only]

CC @envoyproxy/api-shepherds: Your approval is needed for changes made to (api/envoy/|docs/root/api-docs/).
envoyproxy/api-shepherds assignee is @abeyad
CC @envoyproxy/api-watchers: FYI only for changes made to (api/envoy/|docs/root/api-docs/).

🐱

Caused by: #41215 was opened by wtzhang23.

see: more, trace.

[wtzhang23]

Not needed. See envoyproxy/dynamic-modules-examples#45 to see how the namespace prefix is stripped. Users can just specify the full metric name.