4.18 kernel support

[grcevski]

Adding support for kernel 4.18 is the most frequently requested feature because of older RedHat LTS versions. Adding support for 4.18 needs work on few fronts:

• We need to switch from using ringbuffers to perf buffers.
• We need to ensure we can pull BTF symbols in a productized way. (since BTF will not be present on 4.18)
• There might be issues with reading the iovec structures.

[grcevski]

Thanks for reopening, I accidentally moved the issue in the wrong column in the project, to completed instead of in progress.

[rafaelroquetto]

Recent RHEL 4.18 kernels are heavily backported and provide the necessary infrastructure required by Beyla. We have decided to provide supports only for these select RHEL kernels rather than vanilla 4.18, as it covers most people still on that kernel version.

See #1175 for further context.