feat(axiom): add support for regional edge endpoints in AxiomConfig (#24037)

* feat(axiom sink): Add regional edge support with smart URL handling

Introduces optional `region` field for regional edge domains and enhances
`url` field with intelligent path detection. URLs with custom paths are
used as-is, while URLs without paths maintain backwards compatibility by
appending the legacy path format.

Priority: url > region > default cloud endpoint

Fully backwards compatible with existing configurations.

* cargo fmt

* refactor(axiom): Axiom sink configuration and integration tests

- Moved the Axiom sink configuration and integration tests to a new module `axiom` under the `sinks` directory.
- Implemented `UrlOrRegion` struct to manage Axiom endpoint configurations, ensuring validation between URL and region settings.
- Moved the integration tests to a new module `integration_tests` under the `axiom` module.
- Updated documentation for the Axiom sink configuration in the generated CUE files to reflect new fields and usage examples.

* cargo fmt

* fix(axiom): Update integration tests to include SinkConfig and UrlOrRegion

* Update website/cue/reference/components/sinks/generated/axiom.cue

Co-authored-by: domalessi <[email protected]>

* fix: Fix wording

* fix(axiom): Make AxiomConfig fields public

---------

Co-authored-by: Pavlos Rontidis <[email protected]>
Co-authored-by: domalessi <[email protected]>

Author: 3 people

changelog.d/axiom_regional_edges.feature.md

@@ -0,0 +1,3 @@
+The `axiom` sink now supports regional edges for data locality. A new optional `region` configuration field allows you to specify the regional edge domain (e.g., `eu-central-1.aws.edge.axiom.co`). When configured, data is sent to `https://{region}/v1/ingest/{dataset}`. The `url` field now intelligently handles paths: URLs with custom paths are used as-is, while URLs without paths maintain backwards compatibility by appending `/v1/datasets/{dataset}/ingest`.
+
+authors: toppercodes