Replace plain text application secret with a copy button

📖 What does this MR do?

Related to #332844 (closed)

Currently when you create an application (Admin, User, or Group) it displays the secret in plain text on the screen. To improve security this MR replaces the plain text secret with a copy button.

📈 Future iterations

• #338242
• #338243 (closed)

💻 How to setup and validate locally

Admin applications

1. Navigate to Menu -> Admin -> Applications
2. Click New application and complete the form

Group applications

1. Create a group
2. Navigate to Settings -> Applications and complete the form

User applications

1. Click your avatar in the upper right corner and select Preferences
2. Click Applications in the sidebar and complete the form

📷 Screenshots

View	Before	After
Admin applications
Group applications
User applications

🚦 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

Does this MR contain changes to processing or storing of credentials or tokens, authorization and authentication methods or other items described in the security review guidelines? If not, then delete this Security section.

• 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