Provide more refined configuration of Devops agent

What type of PR is this?

/area devops /kind feature

What this PR does / why we need it:

I provide three options for devops.agent.config configuration in ClusterConfiguration: default(or leave empty), high and custom, each representing a different limit level respectively, except for the custom option.

After doing this,

• Users can configure different limit levels according to their own actual situation to improve the stability and efficiency of the system.
• Once user has specified the custom option, any subsequent changes will not take effect.
• Even if uses upgrade from the old version, it will not have any impact.

The main processing flow is as follow:

Which issue(s) this PR fixes:

None

Special notes for reviewers:

Test docker image: johnniang/ks-installer:agent-config-level

Does this PR introduced a user-facing change?

Additional documentation, usage docs, etc.: