Use client-side redirect for collate docs

The functions and operators page is auto-generated from cockroach.
That page includes invalid links to collatedstring.html. Even with
a server-side redirect from collatedstring.html to collate.html,
the build fails because the link checker we run doesn't know about
the server-side redirects.

For the time-being, I'm putting the client-side redirects back in
place. I'll open a PR in the cockroach repo to fix the links
in the generated docs and then remove the client-side redirects.

_redirects

@@ -293,13 +293,6 @@ layout: null
 /docs/v21.1/start-a-local-cluster-in-docker.html /docs/v21.1/start-a-local-cluster-in-docker-mac.html 301
 /docs/stable/start-a-local-cluster-in-docker.html /docs/stable/start-a-local-cluster-in-docker-mac.html 301
 /docs/*/general-troubleshooting.html /docs/*/common-errors.html 301
-/docs/v2.0/collatedstring.html /docs/v2.0/collate.html 301
-/docs/v2.1/collatedstring.html /docs/v2.1/collate.html 301
-/docs/v19.1/collatedstring.html /docs/v19.1/collate.html 301
-/docs/v19.2/collatedstring.html /docs/v19.2/collate.html 301
-/docs/v20.1/collatedstring.html /docs/v20.1/collate.html 301
-/docs/v20.2/collatedstring.html /docs/v20.2/collate.html 301
-/docs/v21.1/collatedstring.html /docs/v21.1/collate.html 301
 /docs/v2.1/show-create-view.html /docs/v2.1/show-create.html 301
 /docs/v19.1/show-create-view.html /docs/v19.1/show-create.html 301
 /docs/v19.2/show-create-view.html /docs/v19.2/show-create.html 301

v19.1/collate.md

@@ -2,6 +2,7 @@
 title: COLLATE
 summary: The COLLATE feature lets you sort strings according to language- and country-specific rules.
 toc: true
+redirect_from: collatedstring.html
 ---
 
 The `COLLATE` feature lets you sort [`STRING`](string.html) values according to language- and country-specific rules, known as collations.

v19.2/collate.md

@@ -2,6 +2,7 @@
 title: COLLATE
 summary: The COLLATE feature lets you sort strings according to language- and country-specific rules.
 toc: true
+redirect_from: collatedstring.html
 ---
 
 The `COLLATE` feature lets you sort [`STRING`](string.html) values according to language- and country-specific rules, known as collations.

v2.0/collate.md

@@ -2,6 +2,7 @@
 title: COLLATE
 summary: The COLLATE feature lets you sort strings according to language- and country-specific rules.
 toc: true
+redirect_from: collatedstring.html
 ---
 
 The `COLLATE` feature lets you sort [`STRING`](string.html) values according to language- and country-specific rules, known as collations.

v2.1/collate.md

@@ -2,6 +2,7 @@
 title: COLLATE
 summary: The COLLATE feature lets you sort strings according to language- and country-specific rules.
 toc: true
+redirect_from: collatedstring.html
 ---
 
 The `COLLATE` feature lets you sort [`STRING`](string.html) values according to language- and country-specific rules, known as collations.

v20.1/collate.md

@@ -2,6 +2,7 @@
 title: COLLATE
 summary: The COLLATE feature lets you sort strings according to language- and country-specific rules.
 toc: true
+redirect_from: collatedstring.html
 ---
 
 The `COLLATE` feature lets you sort [`STRING`](string.html) values according to language- and country-specific rules, known as collations.

v20.2/collate.md

@@ -2,6 +2,7 @@
 title: COLLATE
 summary: The COLLATE feature lets you sort strings according to language- and country-specific rules.
 toc: true
+redirect_from: collatedstring.html
 ---
 
 The `COLLATE` feature lets you sort [`STRING`](string.html) values according to language- and country-specific rules, known as collations.

v21.1/collate.md

@@ -2,6 +2,7 @@
 title: COLLATE
 summary: The COLLATE feature lets you sort strings according to language- and country-specific rules.
 toc: true
+redirect_from: collatedstring.html
 ---
 
 The `COLLATE` feature lets you sort [`STRING`](string.html) values according to language- and country-specific rules, known as collations.