Backport of NET-581 - Added vault namespace in helm into release/1.2.x

[hc-github-team-consul-core]

Backport

This PR is auto-generated from #2841 to be assessed for backporting due to the inclusion of the label backport/1.2.x.

🚨

Warning automatic cherry-pick of commits failed. If the first commit failed,
you will see a blank no-op commit below. If at least one commit succeeded, you
will see the cherry-picked commits up to, not including, the commit where
the merge conflict occurred.

The person who merged in the original PR is:
@absolutelightning
This person should manually cherry-pick the original PR into a new backport PR,
and close this one when the manual backport PR is merged in.

merge conflict error: unable to process merge commit: "c7342840f1e1f0ca6ec613332ae3dfdd12be19cc", automatic backport requires rebase workflow

The below text is copied from the body of the original PR.

---

Changes proposed in this PR:

• Adds vaultNamespace in secretsBackend.vault in values.yaml
• This namespace is used for Vault namespace, this introduces one more way to specify namespace other than
  "{"connect": [{ "ca_config": [{ "namespace": "value"}]}]}" in connectCA.additionalConfig
• If vaultNamespace is present, it automatically adds annotation below to the templates.

    vault:
      agentAnnotations: |
        vault.hashicorp.com/namespace: vaultNamespace

How I've tested this PR:
a. CI
b. Updated test TestVault_VaultNamespace
Test Steps -

1. kind create cluster --name=dc1
2. kind create cluster --name=dc2
3. cd acceptance/test/vault
4. go test ./... -p 1 -timeout 2h -failfast -no-cleanup-on-failure -debug-directory=/tmp/debug -use-kind -enable-multi-cluster -kube-contexts=kind-dc1,kind-dc2  -run ^TestVault

Output -

asheshvidyut@absolutelightning-H2GX766V9T acceptance/tests (NET-581-Configure-Vault-namespaces-for-Connect-CA-via-Helm-Stanza) » go test ./... -p 1 -timeout 2h -failfast -no-cleanup-on-failure -debug-directory=/tmp/debug -use-kind -enable-multi-cluster -kube-contexts=kind-dc1,kind-dc2  -run ^TestVault
ok  	github.com/hashicorp/consul-k8s/acceptance/tests/api-gateway	0.492s [no tests to run]
ok  	github.com/hashicorp/consul-k8s/acceptance/tests/basic	0.547s [no tests to run]
ok  	github.com/hashicorp/consul-k8s/acceptance/tests/cli	0.529s [no tests to run]
ok  	github.com/hashicorp/consul-k8s/acceptance/tests/cloud	0.565s [no tests to run]
ok  	github.com/hashicorp/consul-k8s/acceptance/tests/config-entries	0.524s [no tests to run]
ok  	github.com/hashicorp/consul-k8s/acceptance/tests/connect	0.556s [no tests to run]
ok  	github.com/hashicorp/consul-k8s/acceptance/tests/consul-dns	0.543s [no tests to run]
ok  	github.com/hashicorp/consul-k8s/acceptance/tests/example	0.540s
ok  	github.com/hashicorp/consul-k8s/acceptance/tests/ingress-gateway	0.553s [no tests to run]
ok  	github.com/hashicorp/consul-k8s/acceptance/tests/metrics	0.555s [no tests to run]
ok  	github.com/hashicorp/consul-k8s/acceptance/tests/partitions	0.561s [no tests to run]
ok  	github.com/hashicorp/consul-k8s/acceptance/tests/peering	0.568s [no tests to run]
ok  	github.com/hashicorp/consul-k8s/acceptance/tests/sameness	0.552s
ok  	github.com/hashicorp/consul-k8s/acceptance/tests/snapshot-agent	0.572s [no tests to run]
ok  	github.com/hashicorp/consul-k8s/acceptance/tests/sync	0.554s [no tests to run]
ok  	github.com/hashicorp/consul-k8s/acceptance/tests/terminating-gateway	0.553s [no tests to run]
ok  	github.com/hashicorp/consul-k8s/acceptance/tests/vault	916.339s
ok  	github.com/hashicorp/consul-k8s/acceptance/tests/wan-federation	0.587s [no tests to run]

How I expect reviewers to test this PR:

Checklist:

• Tests added
• CHANGELOG entry added

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Overview of commits

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