Add subpath/route-prefix support

[AlinaGoaga]

Closes #3440

Using:

• Expose OSS static asset handling to unify OSS/EE serving weave-gitops#4007 (needs merging prior to merging of this current branch)
• https://github.com/weaveworks/weave-gitops-enterprise/tree/ui-on-subpath

What changed?

Enables support for running under weave-gitops-enterprise under a subpath e.g. example.com/weave-gitops-enterprise/ in the UI router

Why was this change made?

Possibility to expose weave-gitops-enterprise dashboard under subpaths.

How was this change implemented?

See comments in Core weaveworks/weave-gitops#3992 (subpath PR in Core)

How did you validate the change?

• Explain how a reviewer can verify the change themselves
• uncomment the additionalArgs in tools/dev-values.yaml
• tilt up
• open http://localhost:8000/
• note you are redirected to http://localhost:8000/weave-gitops-enterprise/ and the UI should all work

TBD: test with Ingress (brought over the script to create a kind cls with ingress however we need to adjust the tilt startup script to use this one rather than the standard wge-dev).

• Integration tests -- what is covered, what cannot be covered;
  or, explain why there are no new tests

• Unit tests -- what is covered, what cannot be covered; are
  there tests that fail without the change?

Unit tests can be found in Core for the utils used in EE which we import from there.

Release notes

Documentation Changes

Add a website/docs/enterprise/getting-started/run-ui-subpath.mdx for EE in docs.
weaveworks/weave-gitops#4156

Other follow ups

[foot]

🔥 !

• GitAuth needs to be pulled in too I think
• nitpicking on the names const { clustersService } = useEnterpriseClients()? idk, wdyt?

Tested ingress though w/ INSTALL_NGINX_INGRESS=1 DELETE_GITOPS_DEV_REPO=1 ./tools/reboot.sh

and tilt up

and http://localhost:30080/weave-gitops-enterprise and it all works 🎉

[foot]

🔥 ! Working great

• added some tweaks to get gitlab PRs working.
• added some more withBasePaths around the place where I could see window.location being used, not sure if we need those error handlers anymore though.

[foot]

💯