Update embedded snippet file links to open in new tab

What does this MR do?

This fixes a Content Security Policy error when clicking on the file links in an embedded snippet while its embedded in another website.

Screenshots (strongly suggested)

Before:

https://jsfiddle.net/x7dtrogm/

Clicking on either of these links in the header:

you will get a crashed iframe and an error in the console:

Refused to frame 'https://gitlab.com/' because an ancestor violates the following Content Security Policy directive: "frame-ancestors 'self'".

After:

Link successfully opens in new tab

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.

Security

no security concerns