Sanitize custom permalink settings

[webtrainingwheels]

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Describe the bug
Since version 3.13 we are using the permalink structure in $rocket_permalink_structure
If the customer is using a custom structure with a weird input, it can cause a fatal error, because we don't sanitize this.
Example of an input that causes problems: /'/%year%/%monthnum%/%day%/%postname%/'
https://i.imgur.com/2rZIyea.png

To Reproduce
Steps to reproduce the behavior:

1. Go to Settings → Permalinks. Choose custom structure and enter: /'/%year%/%monthnum%/%day%/%postname%/'
2. Activate WP Rocket
3. Check the wp-rocket-config file and you will see:
   $rocket_permalink_structure = '/'/%year%/%monthnum%/%day%/%postname%/'';
4. Go to the frontend of the site and you will have a critical error.
5. In the error log you will see: Parse error: syntax error, unexpected token "%" in /wp-content/wp-rocket-config/yourdomain.php on line 82

Expected behavior
If WordPress accepts a permalink structure, we should be able to as well. We should sanitize this so it doesn't cause an error, even if it's an edge case.

Screenshots
If applicable, add screenshots to help explain your problem.

Additional context
Ticket: https://secure.helpscout.net/conversation/2207611833/412789?folderId=377611
Slack:https://wp-media.slack.com/archives/C43T1AYMQ/p1682465607573189

Backlog Grooming (for WP Media dev team use only)

• Reproduce the problem
• Identify the root cause
• Scope a solution
• Estimate the effort

[piotrbak]

@wp-media/php What do you think about that sanitization? Do you see this one risky?

[Tabrisrp]

We can escape the ' character before adding the structure to the file, this should avoid the error. We can test with that solution if the behaviour is correctly preserved.

[jeawhanlee]

Reproduce the problem ✅

I was able to reproduce the problem.

Identify the root cause ✅

Unescaped quotes in the config file.

Scope a solution ✅

Like @Tabrisrp proposed, we can escape these kind of quotes before adding the permalink structure to the config file
on this line

wp-rocket/inc/functions/files.php

Line 158 in 10e82c0

$buffer .= '$rocket_permalink_structure = \'' . get_option( 'permalink_structure' ) . "';\n";

:
we can escape like this wp_slash( get_option( 'permalink_structure' ) )

Though for a structure like this we will not be redirecting with a trailing slash.

Estimate the effort ✅

[XS]