SUBMARINE-578. Update /docs/userdocs/k8s/api/experiment.md

[kevin85421]

What is this PR for?

Update /docs/userdocs/k8s/api/experiment.md

In the document, every curl command cannot work properly.
For example, I execute curl -X GET http://127.0.0.1/api/v1/experiment to list all experiments,
and the response is "404 Not Found". Therefore, I modify 127.0.0.1 to 127.0.0.1:8080, and get the expected response as shown in the following figure.

What type of PR is it?

Documentation

Todos

What is the Jira issue?

https://issues.apache.org/jira/browse/SUBMARINE-578

How should this be tested?

• Step1: Follow the document to deploy Submarine on k8s.
• Step2: Port forward

kubectl port-forward svc/submarine-server 8080:8080

• Step3: Execute the following curl commands

# Get "404 Not Found"
curl -X GET http://127.0.0.1/api/v1/experiment
# Get expected response
curl -X GET http://127.0.0.1:8080/api/v1/experiment

Screenshots (if appropriate)

Questions:

• Does the licenses files need update? No
• Is there breaking changes for older versions? No
• Does this needs documentation? No

[xunliu]

LGTM