buildkite: support for npcap or urgency releases (backport #556)

[mergify]

See https://github.com/elastic/golang-crossbuild/blob/main/NPCAP.md#backports

There is the concept of major.minor.patch.x for cases that need to change an existing Golang Crossbuild release with something else.

We have used that in some cases such as the NPCAP in the past, and recently at #554

But the existing conditions in the BK pipeline didn't allow to actually proceed.

In my view, we should allow running releases for:

• main
• ^[0-9]+.[0-9]+$
• ^[0-9]+.[0-9]+

This should help with cases such as:

• main
• 1.24
• 1.24.0.x

---

This is an automatic backport of pull request #556 done by [Mergify](https://mergify.com).

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: 7a54eee

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: 7a54eee

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: 7a54eee