Adds new Cilium subcommand: cilium encrypt status and cilium encrypt flush

[h3llix]

Fixes: #14638

cilium encrypt status displays information on the current status of the IPSec configuration while cilium encrypt flush flushes the current XFRM States.

Here is the cli output:

[pchaigno]

Looks good. I only have minor comments.

We will also need unit tests for the helper functions in encrypt_status.go: getXfrmStats, countUniqueIPsecKeys, maxSequenceNumber. You can check examples for other commands in the same directory as that file.

[twpayne]

Code looks good, looks like you need to run make -C Documentation update-cmdref to update the docs following the changes to the CLI option descriptions.

[rolinh]

LGTM (but with some nits below)

[pchaigno]

A couple remaining nits below. The output in case of failure could also be improved a bit. For example, this is what I get just after having run cilium encrypt flush:

Encryption: IPsec                     
Keys in use: 0                         
Max Seq. Number: /0xffffffff
Errors: 9                         
XfrmInNoStates: 9

For Max Seq. Number we could either default to a 0 value or even explicitly state N/A when they are no oseq matches. XfrmInNoStates should also be indented for clarity.

[pchaigno]

Found a couple errors while testing. We could also cover a couple more cases in the unit tests.

General remarks:

• Commit fix(cilium encrypt): fix helper functions and minor nits should be squashed in the relevant previous commits. For example, if there is a fix to helper function A, then that fix should be in the commit that introduced function A.
• We don't usually have the format feat(), test(), etc. in Cilium. I like it, but I think it would be best to drop it for consistency with the rest of the commit history.
• You will need to rebase with latest master. In general, I would advise to always rebase with latest master when you update the branch. That's the best way to keep the branch up-to-date.

[pchaigno]

Only one nit below. LGTM otherwise!

[pchaigno]

The end-to-end tests don't cover those new CLIs and other tests are all passing. All team review requests are covered, sometimes with multiple reviews. Marking ready to merge.