Add optional mapId config for GeoJsonFolder

[MisterGC]

Add optional mapId property to GeoJsonFolder config, allowing users to set a custom map identifier instead of relying on automatic derivation from the folder path.

• Add mapId to the JSON schema for GeoJsonFolder
• Pass mapId to GeoJsonSource constructor (falls back to path-derived ID if not provided)

Closes #142

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

Package	Line Rate	Branch Rate	Health
libs.geojsonsource.include.geojsonsource	100%	50%	✔
libs.geojsonsource.src	76%	43%	➖
libs.gridsource.include.gridsource	0%	0%	❌
libs.gridsource.src	0%	0%	❌
libs.http-datasource.src	57%	30%	➖
libs.http-service.include.mapget.http-service	100%	100%	✔
libs.http-service.src	58%	20%	➖
libs.logging.include.mapget	8%	4%	❌
libs.model.include.mapget.model	54%	32%	➖
libs.model.src	62%	33%	➖
libs.service.include.mapget.service	40%	0%	❌
libs.service.src	78%	41%	➖
Summary	57% (4175 / 7343)	28% (4164 / 14628)	➖

Minimum allowed line rate is 50%