Cleanup admission-controllers page

This PR fixes several things in the admission-controllers page:

- The `PodSecurity` plugin is enabled by default, but it was not listed so;
- The `apiserver.config.k8s.io/v1alpha1` has been deprecated since v1.17, we are still documenting it side by side with the `apiserver.config.k8s.io/v1` API group;
- The `eventratelimit.admission.k8s.io/v1alpha1` API could use a better reference rather than the design doc; **The imagepolicy.v1alpha1 API is not documented anywhere, I'll add it later on.**
- There are statements about future, which should be removed;
- We are supposed refer to the `LimitRage` API reference rather than pointing users to the design docs;
- We are supposed refer to the `ResourceQuota` API reference rather than pointing users to the design docs;
- There are long lines in the page source which could have been wrapped properly.

content/en/docs/reference/config-api/apiserver-eventratelimit.v1alpha1.md

@@ -0,0 +1,121 @@
+---
+title: Event Rate Limit Configuration (v1alpha1)
+content_type: tool-reference
+package: evenratelimit.admission.k8s.io/v1alpha1
+auto_generated: true
+---
+
+
+## Resource Types 
+
+
+- [Configuration](#evenratelimit-admission-k8s-io-v1alpha1-Configuration)
+  
+    
+
+## `Configuration`     {#evenratelimit-admission-k8s-io-v1alpha1-Configuration}
+    
+
+
+<p>Configuration provides configuration for the EventRateLimit admission
+controller.</p>
+
+
+<table class="table">
+<thead><tr><th width="30%">Field</th><th>Description</th></tr></thead>
+<tbody>
+    
+<tr><td><code>apiVersion</code><br/>string</td><td><code>evenratelimit.admission.k8s.io/v1alpha1</code></td></tr>
+<tr><td><code>kind</code><br/>string</td><td><code>Configuration</code></td></tr>
+    
+  
+<tr><td><code>limits</code> <B>[Required]</B><br/>
+<a href="#evenratelimit-admission-k8s-io-v1alpha1-Limit"><code>[]Limit</code></a>
+</td>
+<td>
+   <p>limits are the limits to place on event queries received.
+Limits can be placed on events received server-wide, per namespace,
+per user, and per source+object.
+At least one limit is required.</p>
+</td>
+</tr>
+</tbody>
+</table>
+
+## `Limit`     {#evenratelimit-admission-k8s-io-v1alpha1-Limit}
+    
+
+**Appears in:**
+
+- [Configuration](#evenratelimit-admission-k8s-io-v1alpha1-Configuration)
+
+
+<p>Limit is the configuration for a particular limit type</p>
+
+
+<table class="table">
+<thead><tr><th width="30%">Field</th><th>Description</th></tr></thead>
+<tbody>
+    
+  
+<tr><td><code>type</code> <B>[Required]</B><br/>
+<a href="#evenratelimit-admission-k8s-io-v1alpha1-LimitType"><code>LimitType</code></a>
+</td>
+<td>
+   <p>type is the type of limit to which this configuration applies</p>
+</td>
+</tr>
+<tr><td><code>qps</code> <B>[Required]</B><br/>
+<code>int32</code>
+</td>
+<td>
+   <p>qps is the number of event queries per second that are allowed for this
+type of limit. The qps and burst fields are used together to determine if
+a particular event query is accepted. The qps determines how many queries
+are accepted once the burst amount of queries has been exhausted.</p>
+</td>
+</tr>
+<tr><td><code>burst</code> <B>[Required]</B><br/>
+<code>int32</code>
+</td>
+<td>
+   <p>burst is the burst number of event queries that are allowed for this type
+of limit. The qps and burst fields are used together to determine if a
+particular event query is accepted. The burst determines the maximum size
+of the allowance granted for a particular bucket. For example, if the burst
+is 10 and the qps is 3, then the admission control will accept 10 queries
+before blocking any queries. Every second, 3 more queries will be allowed.
+If some of that allowance is not used, then it will roll over to the next
+second, until the maximum allowance of 10 is reached.</p>
+</td>
+</tr>
+<tr><td><code>cacheSize</code><br/>
+<code>int32</code>
+</td>
+<td>
+   <p>cacheSize is the size of the LRU cache for this type of limit. If a bucket
+is evicted from the cache, then the allowance for that bucket is reset. If
+more queries are later received for an evicted bucket, then that bucket
+will re-enter the cache with a clean slate, giving that bucket a full
+allowance of burst queries.</p>
+<p>The default cache size is 4096.</p>
+<p>If limitType is 'server', then cacheSize is ignored.</p>
+</td>
+</tr>
+</tbody>
+</table>
+
+## `LimitType`     {#evenratelimit-admission-k8s-io-v1alpha1-LimitType}
+    
+(Alias of `string`)
+
+**Appears in:**
+
+- [Limit](#evenratelimit-admission-k8s-io-v1alpha1-Limit)
+
+
+<p>LimitType is the type of the limit (e.g., per-namespace)</p>
+
+
+
+