docs: use pipefail option in shell commands to prevent accidental deletions

Description

When using a pipe in shell commands (|) it is critical that the pipefail option is used, otherwise the second command in the pipeline silently overwrites any errors from the first command. Argo CD will then treat the stdout output as valid (even if it is empty), which can have catastrophic effects: deleting all resources belonging to the Application/ApplicationSet.

Several users have already been hit by this: https://github.com/argoproj-labs/argocd-vault-plugin/issues/533

Therefore I believe it is very important that the correct commands are shown in the documentation.

Fixes: https://github.com/argoproj-labs/argocd-vault-plugin/issues/533

Checklist

Please make sure that your PR fulfills the following requirements:

[x] Reviewed the guidelines for contributing to this repository
[x] The commit message follows the Conventional Commits Guidelines.
[ ] Tests for the changes have been updated
[ ] Are you adding dependencies? If so, please run go mod tidy -compat=1.21 to ensure only the minimum is pulled in.
[x] Docs have been added / updated
[ ] Optional. My organization is added to USERS.md.

Type of Change

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] New tests
[ ] Build/CI related changes
[x] Documentation content changes
[ ] Other (please describe)

argoproj-labs / argocd-vault-plugin