[Feature] Support of self hosted reverse geocode service as immich's reverse geocode backend alternative

[ByeongsuPark]

I have searched the existing feature requests, both open and closed, to make sure this is not a duplicate request.

• Yes

The feature

Currently, It seems like that immich relies on geo data from geonames.org to enrich photo metadata with location information. However, as reported in issues(#10850, #17905), The accuracy and reliability of these data can be inconsistent, often resulting in incorrect or imprecise location names.
This leads to a inconvenience of user experience, especially for those who heavily rely on geolocation data for organizing and browsing their photo libraries.

To address this issue, I’d like to propose adding support for a self-hosted reverse geocoding backend (e.g., Nominatim) as an optional alternative to the current reverse geocoding mechanism.

Benefits

Improved accuracy and consistency of location data, especially when using high-quality or regionally specialized data sources.

Proposed Implementation

• Introduce configuration options for specifying a custom reverse geocoding service URL.
• Optionally allow users to choose between multiple providers via settings or environment variables.

Platform

• Server
• Web
• Mobile

[bo0tzz]

We have no plans to add support for external APIs, see #8551 (reply in thread).