Update behavior for the ssh config/ca endpoint when a CA exists (#684)

The docs mentioned that the values would be overwritten on the SSH
config/ca endpoint but we actually error out to the end user, telling
them they must delete before the update will take place. Update our docs
to match the code.

Author: stevendpclark

content/vault/v1.16.x/content/api-docs/secret/ssh.mdx

@@ -558,8 +558,10 @@ $ curl \
 ## Submit CA information
 
 This endpoint allows submitting the CA information for the secrets engine via an SSH
-key pair. _If you have already set a certificate and key, they will be
-overridden._
+key pair. If you call submit CA with an existing certificate or key, the
+endpoint returns an error. To update existing values, call the delete CA
+information endpoint before calling the submit endpoint.
+
 
 | Method | Path             |
 | :----- | :--------------- | -------------------------- |

content/vault/v1.17.x/content/api-docs/secret/ssh.mdx

@@ -562,8 +562,9 @@ $ curl \
 ## Submit CA information
 
 This endpoint allows submitting the CA information for the secrets engine via an SSH
-key pair. _If you have already set a certificate and key, they will be
-overridden._
+key pair. If you call submit CA with an existing certificate or key, the
+endpoint returns an error. To update existing values, call the delete CA
+information endpoint before calling the submit endpoint.
 
 | Method | Path             |
 | :----- | :--------------- | -------------------------- |

content/vault/v1.18.x/content/api-docs/secret/ssh.mdx

@@ -562,8 +562,9 @@ $ curl \
 ## Submit CA information
 
 This endpoint allows submitting the CA information for the secrets engine via an SSH
-key pair. _If you have already set a certificate and key, they will be
-overridden._
+key pair. If you call submit CA with an existing certificate or key, the
+endpoint returns an error. To update existing values, call the delete CA
+information endpoint before calling the submit endpoint.
 
 | Method | Path             |
 | :----- | :--------------- | -------------------------- |

content/vault/v1.19.x/content/api-docs/secret/ssh.mdx

@@ -559,8 +559,9 @@ $ curl \
 ## Submit CA information
 
 This endpoint allows submitting the CA information for the secrets engine via an SSH
-key pair. _If you have already set a certificate and key, they will be
-overridden._
+key pair. If you call submit CA with an existing certificate or key, the
+endpoint returns an error. To update existing values, call the delete CA
+information endpoint before calling the submit endpoint.
 
 | Method | Path             |
 | :----- | :--------------- | -------------------------- |

content/vault/v1.20.x/content/api-docs/secret/ssh.mdx

@@ -559,8 +559,9 @@ $ curl \
 ## Submit CA information
 
 This endpoint allows submitting the CA information for the secrets engine via an SSH
-key pair. _If you have already set a certificate and key, they will be
-overridden._
+key pair. If you call submit CA with an existing certificate or key, the
+endpoint returns an error. To update existing values, call the delete CA
+information endpoint before calling the submit endpoint.
 
 | Method | Path             |
 | :----- | :--------------- | -------------------------- |