fix: Set seccomp profiles and grant SAs necessary premissions to run

[JoaoBraveCoding]

When running in namespace with Pod Security Standard profile "restricted"
we need to set RunAsNonRoot and SeccompProfile to all workloads running
on that namespace. Futhermore on OpenShift to run with a SeccompProfile
set we need to grant service accounts premisisons to use the SCC
nonroot-v2
Fixes #149

[JoaoBraveCoding]

So CI was failing because if I set on the AM deployment the securityContext: runAsNonRoot: true then the AM pods do not start with the following error:

 Warning  Failed     3s (x5 over 37s)  kubelet            Error: container has runAsNonRoot and image has non-numeric user (nobody), cannot verify user is non-root (pod: "alertmanager-self-scrape-0_e2e-tests(6840fcd1-b25a-4d95-bcb4-87da5ded49d8)", container: config-reloader)

I checked and indeed the AM dockerimage uses nobody... but I'm afraid I might be missing something because it feels weird to me that if the problem is indeed with the dockerimage that only now the problem is surfacing. Do know anything about this @simonpasquier

[sthaha]

Looks good to me 😍
I will let @simonpasquier approve the PR.

[sthaha]

removing approval for @simonpasquier to approve this PR.
We should consider releasing as soon as this merges.

I will let Simon who understands this better approve the PR

[JoaoBraveCoding]

For traceability: After talking with @simonpasquier offline we decided to add to the Alertmanager deployment a arbitrary UID in order to solve the issue above [1] and future prof the Alertmanager deployment if in the future we have to add persistent storage.

[1] #154 (comment)