fix(config): Warn on invalid characters in datacenter property leading to incompatible DNS names

[arnabkaycee]

Description

Non-compliant characters lead to invalid DNS names that are incompatible with externalized PKI Certificate generation.

Testing & Reproduction steps

• Start consul with invalid characters in datacenter property.
• Create tls certificates using CLI Commands. Consul does not warn/fail.
• When using other PKI engines to generate certificates with SAN as <service-name>.service.<datacenter>.consul PKI generation usually fails because of invalid characters in datacenter field.
• It is not possible to change datacenter name as it is an initial bootstrapping configuration of consul. One has to migrate entire data.

Links

PR Checklist

• updated test coverage
• external facing docs updated
• appropriate backport labels added
• not a security concern

[sreeram77]

LGTM!

[hashicorp-cla-app]

All committers have signed the CLA.

[hc-github-team-consul-core]

📣 Hi @arnabkaycee! a backport is missing for this PR [22382] for versions [1.18,1.19,1.20,1.21] please perform the backport manually and add the following snippet to your backport PR description:

<details>
	<summary> Overview of commits </summary>
		- <<backport commit 1>>
		- <<backport commit 2>>
		...
</details>

[hc-github-team-consul-core]

📣 Hi @arnabkaycee! a backport is missing for this PR [22382] for versions [1.18,1.19,1.20,1.21] please perform the backport manually and add the following snippet to your backport PR description:

<details>
	<summary> Overview of commits </summary>
		- <<backport commit 1>>
		- <<backport commit 2>>
		...
</details>

[hc-github-team-consul-core]

📣 Hi @arnabkaycee! a backport is missing for this PR [22382] for versions [1.18,1.19,1.20,1.21] please perform the backport manually and add the following snippet to your backport PR description:

<details>
	<summary> Overview of commits </summary>
		- <<backport commit 1>>
		- <<backport commit 2>>
		...
</details>