refactor(tools): allow specifying replacement start/end (renovatebot#41250)

As part of future changes, we need to be able to specify the start/end
of replacements in documentation, as we have multiple entries in the
same page.

We can also rename the variable so it's clearer that it's the default
value, not the current scoped value.

Author: jamietanna

tools/docs/utils.ts

@@ -4,9 +4,9 @@ import { regEx } from '../../lib/util/regex.ts';
 import { capitalize } from '../../lib/util/string.ts';
 import { readFile } from '../utils/index.ts';
 
-const replaceStart =
+const defaultReplaceStart =
   '<!-- Autogenerate in https://github.com/renovatebot/renovate -->';
-const replaceStop = '<!-- Autogenerate end -->';
+const defaultReplaceStop = '<!-- Autogenerate end -->';
 const goodUrlRegex = regEx(/\[(.+?)\]\((.+?)\)/);
 
 export function formatName(input: string): string {
@@ -31,9 +31,16 @@ export function getNameWithUrl(
   return displayName;
 }
 
-export function replaceContent(content: string, txt: string): string {
-  const replaceStartIndex = content.indexOf(replaceStart);
-  const replaceStopIndex = content.indexOf(replaceStop);
+export function replaceContent(
+  content: string,
+  txt: string,
+  opts: {
+    replaceStart: string;
+    replaceStop: string;
+  } = { replaceStart: defaultReplaceStart, replaceStop: defaultReplaceStop },
+): string {
+  const replaceStartIndex = content.indexOf(opts.replaceStart);
+  const replaceStopIndex = content.indexOf(opts.replaceStop);
 
   if (replaceStartIndex < 0) {
     logger.error('Missing replace placeholder');
@@ -42,7 +49,7 @@ export function replaceContent(content: string, txt: string): string {
   return (
     content.slice(0, replaceStartIndex) +
     txt +
-    content.slice(replaceStopIndex + replaceStop.length)
+    content.slice(replaceStopIndex + opts.replaceStop.length)
   );
 }