Ptfe 3083 upgrade docker images

[matthiasL-scality]

This pull request updates the build and configuration to use the OpenResty 1.29.2.1 Alpine image instead of a custom Ubuntu/nginx/LuaJIT build, and makes several related compatibility and performance improvements. The changes modernize the Docker setup, simplify dependencies, and address compatibility issues with LuaJIT 5.2 semantics in OpenResty. Additionally, it improves connection handling and fixes potential deadlocks in GitHub API proxying.

Docker and Build System Modernization:

• Switches the base image in the Dockerfile from ubuntu:xenial with a custom nginx/LuaJIT build to openresty/openresty:1.29.2.1-alpine-fat, greatly simplifying the build process and leveraging a maintained OpenResty distribution.
• Updates LuaJIT bytecode compilation commands to use the OpenResty-provided luajit binary path.
• Adds compatibility symlinks so that existing scripts (start.sh, stop.sh) and configuration paths work unchanged with the new OpenResty layout.
• Loads the ngx_http_xslt_filter_module dynamically in the nginx configuration, as required by the OpenResty Alpine image.

Performance and Connection Handling Improvements:

• Increases keepalive connection pool size, number of requests per connection, and timeout values for upstream S3 backends in nginx.conf.template to improve throughput and resource utilization. [1] [2] [3]
• Sets worker_processes to auto and updates the PID file location for better compatibility and scalability.

Lua Compatibility and Bug Fixes:

• Updates lock handling in github_access.lua to correctly interpret os.execute return values under LuaJIT with Lua 5.2 semantics (used by OpenResty), preventing cache lock logic from always failing.
• Skips authentication checks for internal GitHub API proxy subrequests to prevent deadlocks caused by recursive cache locking.

Other Functional Changes:

• Extends AWS S3 presignature expiration from 60 seconds to 1 hour in compute_aws_s3_signature.lua, allowing for longer-lived presigned URLs.

[bertranddemiddelaer]

LGTM

(and nice work, btw !)