fix(prometheus): add a toggle switch for wasm metrics export

[flrgh]

Summary

Adds a toggle for wasm metrics export to the prometheus plugin.

Issue reference

KAG-5904

[flrgh]

@fffonion can you let me know if this is what you were looking for? It is not possible to control export on a per service/route basis for Wasm. It's a little weird putting a global toggle into a configuration field that is not global, but from what I can tell we're doing something similar with upstream_health_metrics, so I followed suit. We can also go the other route and add a global value to kong.conf.

[fffonion]

@flrgh yes, I think a plugin side of config like this is fine 👍. prometheus is still a plugin not a first class component in kong so putting into kong.conf is indeed weird.

[flrgh]

note: has manual backport/cherry-pick PRs already:

• Kong/kong:release/3.9.x => [backport -> release/3.9.x] fix(prometheus): add a toggle switch for wasm metrics export #13968
• Kong/kong-ee:master => https://github.com/Kong/kong-ee/pull/10930
• Kong/kong-ee:next/3.9.x.x => https://github.com/Kong/kong-ee/pull/10931

[locao]

Suggested change

	[3009000000] = {
	[30010000000] = {

3.9.0 is in code freeze, should we target this to 3.10 or 3.9.1?
Note: I'm not sure that is how we target 3.10, is there a risk we target 3.1.0?