Create pipeline configuration location input

What does this MR do?

This MR adds a new field for the compliance frameworks forms. The new field accepts a project YAML file as an input and will be used to compile custom compliance pipelines.

This MR is part 1 of 2.

Steps	MR
1 - Create the form input	👈 You are here
2 - Add to the compliance forms	!53887 (merged)

Screenshots (strongly suggested)

Video whereby I:

1. Try entering random text - Invalid format error
2. Try entering a bad format - Invalid format error
3. Try entering a non-existant file - Unknown file error
4. Enter a valid file - No error
5. Clear the input - No error

Screen_Recording_2021-02-10_at_16.53.41

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Availability and Testing

This input is being added to a form in part 2. For local testing instructions please see part 2 for how to test this input in-situ as this is probably the simplest and easiest way to test it works as you would expect 🙈

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [-] Security reports checked/validated by a reviewer from the AppSec team

Related to #292696 (closed)