Chained `regex` expressions for relabeling not supported in vmagent CRD

[towolf]

This is a follow up to #730. We noticed that the same issue affects the regex: key in a relabeling config in VMAgent.

The docs state: The regex value can be split into multiple lines for improved readability and maintainability.

However, the CRD does not allow this for regex since it presupposes a string.

[towolf]

@Amper Please take a look? This is nearly the same fix as you did in #738.

[f41gh7]

Must be fixed at v0.43.0 release