feat: set Alias on auto-generated namespace-routing rewrite_tag filters

[ruben-chainalysis]

What this PR does / why we need it:

Auto-generated namespace-routing rewrite_tag filters (created by generateRewriteTagConfig) produce metrics with opaque names like rewrite_tag.0, rewrite_tag.1. This makes it impossible to correlate filter pipeline metrics (fluentbit_filter_records, fluentbit_filter_emit_records) back to the namespace they route for.

This PR sets Alias on each auto-generated rewrite_tag filter using the pattern namespace-routing-<namespace>, so filter metrics become identifiable (e.g. namespace-routing-kube-system instead of rewrite_tag.3).

FluentBit core already uses Alias as the name label in Prometheus metrics (fluent/fluent-bit#4694). CRD-defined filters already support Alias (#356, #370). After #2019 refactored generateRewriteTagConfig to use a filter.RewriteTag struct, CommonParams.AddCommonParams() handles emission, so this is a one-field addition.

Alias uniqueness is guaranteed because Kubernetes namespace names are unique per cluster, so namespace-routing-<ns> cannot collide (fluent/fluent-bit#6076 does not apply).

Which issue(s) this PR fixes:

Fixes #2051

Does this PR introduced a user-facing change?

Auto-generated namespace-routing rewrite_tag filters now set Alias to `namespace-routing-<namespace>`, making filter metrics identifiable by namespace.

Additional documentation, usage docs, etc.:

None

[ruben-chainalysis]

I didn't find the right place to document this, but always happy to put some docs in my PR if you help me with it.

As I said in the linked issue, I don't have an opinion about the naming convention for the Alias, just used the first thing that came to mind. Would putting the namespace name first help for things like dashboard fonts not fitting a very long name? That way the least relevant part of the alias goes at the end.