fix: Update regex parsing for CGroup v1 to match agent spec.

[tippmar-nr]

Updates our container id parsing logic for CGroup v1 to match the agent spec and removes the "fallback" lookup we recently added. The spec requires that we find a line that has cpu in it and contains a 64-character hexadecimal string. The container ID is the 64-character string.

The logic should find a container id of 47cbd16b77c50cbf71401c069cd2189f0e659af17d5a2daca3bddf59d8a870b2 when parsing any of the following lines in /proc/self/cgroup:

1:cpuset:/docker/47cbd16b77c50cbf71401c069cd2189f0e659af17d5a2daca3bddf59d8a870b2
2:cpu:/docker/47cbd16b77c50cbf71401c069cd2189f0e659af17d5a2daca3bddf59d8a870b2
3:cpuacct,cpu:/docker/47cbd16b77c50cbf71401c069cd2189f0e659af17d5a2daca3bddf59d8a870b2
4:memory,cpu,cpuset:/docker/47cbd16b77c50cbf71401c069cd2189f0e659af17d5a2daca3bddf59d8a870b2
5:cpu,cpuacct:/kubepods.slice/kubepods-burstable.slice/kubepods-burstable-pod04f9c4b4_5e71_4a0a_aa3a_f62f089e3f73.slice/cri-containerd-47cbd16b77c50cbf71401c069cd2189f0e659af17d5a2daca3bddf59d8a870b2.scope
6:cpuset:/kubepods.slice/kubepods-burstable.slice/kubepods-burstable-pod04f9c4b4_5e71_4a0a_aa3a_f62f089e3f73.slice/cri-containerd-47cbd16b77c50cbf71401c069cd2189f0e659af17d5a2daca3bddf59d8a870b2.scope

[nr-ahemsath]

Looks good.