Add url base path for stats api and visualizer api endpoints in the env

[tushar994]

Description and Related Issue(s)

added two env variables NEXT_PUBLIC_STATS_API_BASE_PATH and NEXT_PUBLIC_VISUALIZE_API_BASE_PATH, which allows one to set base path for the stats or visualize api endpoints.

Proposed Changes

to add the two env variables in the codebase, following the implementation of pre-existing variable NEXT_PUBLIC_API_BASE_PATH.

Checklist for PR author

• I have tested these changes locally.
• I added tests to cover any new functionality, following this guide
• Whenever I fix a bug, I include a regression test to ensure that the bug does not reappear silently.
• If I have added, changed, renamed, or removed an environment variable, I have updated the list of environment variables in the documentation and made the necessary changes to the validator script according to the guide