fix(pinger): update logic to determine pinger privileged mode

[h3mmy]

Summary

#697 (comment)
Based around fix attempted in #748 since the experimental tagged image worked for pings in non-privileged containers. Apparently it broke for users in root containers, so this PR includes a check for root privilege, albeit a naive one.

As of v5.26.0, ICMP checks still do not work for my (non-root) deployment regardless of whether I add CAP_NET_RAW

Checking individual capabilities will require adding "kernel.org/pub/linux/libs/security/libcap/cap" as a dependency. I'm not sure if you want to add more dependencies for a small check, so I can use some naive logic to check if the app is running as root like checking the EUID == 0

Since SetPrivileged needs to be set to false for non-privileged processes running on linux or darwin, I figured this is a reasonable check unless you are wanting a more precise check with the extra dependency.

Checklist

• Tested and/or added tests to validate that the changes work as intended, if applicable.
• Updated documentation in README.md, if applicable.

[h3mmy]

I can work on adding unit tests once an approach is finalized. I always feel weird making reviews without tests.

[h3mmy]

I played around with precisely checking for CAP_NET_RAW and CAP_NET_ADMIN but a consequence of relying on "kernel.org/pub/linux/libs/security/libcap/cap" is tht CGO_ENABLED would need to be set to 1 instead of 0. I hesitate to bring in a new dependency that will change the build process that way.

I would expect folks running as root without having the uid set to 0 is not super common. In order to be thorough, I decided to check for cap_net_raw by simply testing if opening a raw socket throws a permission error. Let me know if you like or dislike it and I can re-adjust

[h3mmy]

After some testing of the syscall method, it came to light that it won't compile on windows due to the different flags, so I discarded that route and fell back to the initial implementation.

[h3mmy]

I built my own image for testing purposes. Confirmed it works.

repository: ghcr.io/h3mmy/gatus
tag: testing@sha256:87f8e8ea0073d69dd6eecacecf93c55699f2ee9e2e062e547ce4b10b536743d1