fix: allow for large shared_size in kubernetes discovery

[Revolyssup]

Fixes #11857
Currently due to schema validation limitation, setting higher shared_size results in following error

nginx: [error] init_by_lua error: /home/ashish/dev/apisix/apisix/core.lua:21: failed to parse yaml config: invalid discovery kubernetes configuration: object matches none of the required
stack traceback:

Checklist

• I have explained the need for this PR and the problem it solves
• I have explained the changes or the new features added to this PR
• I have added tests corresponding to this change
• I have updated the documentation to reflect this change
• I have verified that this change is backward compatible (If not, please discuss on the APISIX mailing list first)