feat: Extend BGPPeer and enable path modifiers

[nikatza]

Note: this is a breaking change in the API.

The field LocalASNumber enables a router to appear as a member of another AS in addition to its real AS. Most vendors support mechanisms to specify how the device should use this number. This is, however, not specified in OpenConfig[1].

This commit removes LocalASNumber and adds LocalAS, which specifies the local AS number and how this number factors into eBGP announcements.
Specifically, we add three independent boolean flags:

• PrependLocalAS: prepend local-as to inbound routes (default: true)
• PrependGlobalAS: prepend global-as to outbound routes (default: true)
• AcceptEitherAS: accept connections using either AS (default: false)

We opt to follow the Nokia YANG model [2], as it allows us tocover most of the vendors we checked, i.e., Cisco, Juniper, and Arista. This implies that the provider must ensure that the parameter combinations are valid, and reject them with an apistatus error that the controller can wrap into a TerminalError.

Vendor mappings:

Cisco NX-OS/IOS-XR [3,4]:

• PrependLocalAS=false → no-prepend
• PrependLocalAS=false, PrependGlobalAS=false → no-prepend replace-as
• Above + AcceptEitherAS=true → no-prepend replace-as dual-as

Juniper [5]:

• PrependLocalAS=false → no-prepend-global-as
• PrependGlobalAS=false → private
• AcceptEitherAS=true → alias

Arista [6]:

• PrependLocalAS=false → no-prepend
• PrependLocalAS=false, PrependGlobalAS=false → no-prepend replace-as
• Above + AcceptEitherAS=true → no-prepend replace-as fallback

Nokia SR [7]:

• PrependLocalAS → prepend-local-as
• PrependGlobalAS → prepend-global-as
• AcceptEitherAS → not supported

[1] https://openconfig.net/projects/models/schemadocs/yangdoc/openconfig-network-instance.html#network-instances-network-instance-protocols-protocol-bgp-neighbors-neighbor-config-local-as
[2] https://yangbrowser.nokia.com/srlinux/24.10.7/tree?path=%2Fnetworkinstance%5Bname%3D*%5D%2Fprotocols%2Fbgp%2Fneighbor%5Bpeer-address%3D*%5D%2Flocal-as
[3] https://www.cisco.com/c/en/us/td/docs/dcn/nx-os/nexus9000/106x/configuration/unicast-routing-configuration/cisco-nexus-9000-series-nx-os-unicast-routing-configuration-guide/configuring-bgp.html
[4] https://www.cisco.com/c/en/us/td/docs/routers/asr9000/software/routing/configuration/guide/rcg-asr9000/rcg-bgp.html
[5] https://www.juniper.net/documentation/us/en/software/junos/bgp/topics/ref/statement/local-as-edit-protocols-bgp.html
[6] https://www.arista.com/en/um-eos/eos-border-gateway-protocol-bgp
[7] https://documentation.nokia.com/srlinux/24-10/books/routing-protocols/bgp.html

BREAKING CHANGE: LocalASNumber field removed, replaced with LocalAS
struct containing ASNumber, PrependLocalAS, PrependGlobalAS, and
AcceptEitherAS fields.

[github-actions]

Merging this branch will decrease overall coverage

Impacted Packages	Coverage Δ	🤖
github.com/ironcore-dev/network-operator/api/core/v1alpha1	0.00% (ø)
github.com/ironcore-dev/network-operator/internal/controller/core	63.51% (-0.08%)	👎
github.com/ironcore-dev/network-operator/internal/provider/cisco/iosxr	35.93% (ø)
github.com/ironcore-dev/network-operator/internal/provider/cisco/nxos	9.97% (-0.05%)	👎
github.com/ironcore-dev/network-operator/internal/webhook/core/v1alpha1	95.43% (-0.02%)	👎

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Coverage by file

Changed files (no unit tests)

Changed File	Coverage Δ	Total	Covered	Missed	🤖
github.com/ironcore-dev/network-operator/api/core/v1alpha1/bgp_peer_types.go	0.00% (ø)	0	0	0
github.com/ironcore-dev/network-operator/api/core/v1alpha1/zz_generated.deepcopy.go	0.00% (ø)	0	0	0
github.com/ironcore-dev/network-operator/internal/controller/core/bgp_peer_controller.go	58.07% (ø)	322	187	135
github.com/ironcore-dev/network-operator/internal/provider/cisco/iosxr/provider.go	22.00% (ø)	200	44	156
github.com/ironcore-dev/network-operator/internal/provider/cisco/nxos/provider.go	0.06% (-0.00%)	1812 (+13)	1	1811 (+13)	👎
github.com/ironcore-dev/network-operator/internal/webhook/core/v1alpha1/bgppeer_webhook.go	75.00% (-1.92%)	12 (-1)	9 (-1)	3	👎

Please note that the "Total", "Covered", and "Missed" counts above refer to code statements instead of lines of code. The value in brackets refers to the test coverage of that file in the old version of the code.

Changed unit test files

• github.com/ironcore-dev/network-operator/internal/controller/core/bgp_peer_controller_test.go