Replace 3rd party and openresty scripts modules with njs or remove

[rikatz]

Some 3rd party modules and some openresty scripts can be replaced with njs. This would simplify the compilation of our binaries and reduce a bit our dependency on openresty.

The proposed replacements are:

• more_set_headers and more_clear_headers (https://github.com/openresty/headers-more-nginx-module?tab=readme-ov-file#more_set_headers) can be replaced with an njs script to set headers during response time. This can also be kept, if there's a binary compilation. This module is supported by crossplane, and if we have a binary of it is worth keeping
• set_escape_uri - We can do this encoding via js
• auth_digest - Should be verified. Also we should check who is using it, the module seems not being maintained
• substitution doesn't seem to be used and can be removed
• external auth can be rewriten to njs, may have some bigger effort
• auth cache key sets a base64 variable, may be rewritten (need to check)
• server redirects can be rewritten for njs

[longwuyuan]

@elizabeth-dev PTAL at this

[longwuyuan]

#9950

[elizabeth-dev]

/assign

[github-actions]

This is stale, but we won't close it automatically, just bare in mind the maintainers may be busy with other tasks and will reach your issue ASAP. If you have any question or request to prioritize this, please reach #ingress-nginx-dev on Kubernetes Slack.