### What problem does this PR solve?
Added doc for switching elasticsearch to infinity
### Type of change
- [x] New Feature (non-breaking change which adds functionality)
- [x] Documentation Update
### What problem does this PR solve?
This pull request implements the feature mentioned in #3322.
Instead of manually having to edit the `service_conf.yaml` file when
changes have been made to `.env` and mapping it into the docker
container at runtime, a template file is used and the values replaced by
the environment variables from the `.env` file when the container is
started.
### Type of change
- [X] New Feature (non-breaking change which adds functionality)
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Co-authored-by: Kevin Hu <kevinhu.sh@gmail.com>
Co-authored-by: Zhichang Yu <yuzhichang@gmail.com>
