feat: update nginx version to 2.1.5 and enhance downloads configuration(MAPCO-10121)

[almog8k]

This pull request updates the NGINX configuration and Helm chart to improve downloads handling, update dependencies, and add support for Prometheus monitoring. The main changes are a migration from a server-based downloads configuration to a location-based configuration, dependency and image updates, and new configuration options for NGINX extensions and monitoring.

NGINX downloads configuration refactor:

• Replaces the old server-based downloads.conf with a new downloads-location.conf that configures downloads handling using location blocks for both FS and S3 providers, streamlining the configuration and improving maintainability. (helm/config/downloads-location.conf, helm/config/downloads.conf, helm/templates/nginx/nginx-configmap.yaml) [1] [2] [3]
• Updates the ConfigMap and volume mounts to use the new downloads-location.conf file and places it in an extensions directory, reflecting the new configuration structure. (helm/templates/nginx/nginx-configmap.yaml, helm/values.yaml) [1] [2]

Helm values and dependency updates:

• Updates the NGINX Helm dependency and image tags from 2.1.1 to 2.1.5 for both the chart and the container image, ensuring the latest bug fixes and features. (helm/Chart.yaml, helm/values.yaml) [1] [2]
• Adds new configuration options for NGINX extensions, enabling the new downloads location configuration and specifying its filename. (helm/values.yaml)

Prometheus monitoring support:

• Adds configuration for a Prometheus exporter sidecar container to the NGINX deployment, including image settings and resource limits, to enable metrics collection. (helm/values.yaml)