Ability to use local elasticsearch for frontend development

[anupdhml]

Right now for dev use, sangraha frontend defaults to using our prod elasticsearch url. Which is good for getting started on frontend dev easily but there are times when we need to use a local elasticsearch instance (eg: when testing frontend changes that relies on elasticsearch changes too). For that scenario, we should be able to override the dev default (to something like http://localhost:9200)

This can be achieved by sourcing the API_ENDPOINT from an environment variable that can be set to any url we want. Or we can introduce config files for the frontend (which might be useful for other stuff too).