Apply GitLab UI button styles to app/views/projects directory

What does this MR do?

Updates button classes to include gl-button selector within the app/views/projects top level folder.
Fixes a display bug within project settings where the merge requests save changes button was not green

Screenshots (strongly suggested)

File	Before	After
app/views/projects/_home_panel.html.haml	Unable to keep open long enough	unable to keep open long enough
app/views/projects/_last_push.html.haml
app/views/projects/_new_project_fields.html.haml
app/views/projects/_readme.html.haml	Unable to find where this button is	Unable to find button
app/views/projects/_service_desk_settings.html.haml
app/views/projects/_stat_anchor_list.html.haml	Unable to find button	Unable to find button
app/views/projects/_visibility_modal.html.haml	modal wouldn't show	modal wouldn't show
app/views/projects/_wiki.html.haml	Not sure the button is the one on an empty wiki	Not sure the button is the one on an empty wiki
app/views/projects/no_repo.html.haml	Unable to find changed buttons	Unable to find changed buttons
app/views/projects/edit.html.haml (overall)
app/views/projects/edit.html.haml (export)
app/views/projects/edit.html.haml (edit merge request)
app/views/projects/edit.html.haml (run housekeeping)
app/views/projects/edit.html.haml (visibility)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required) not applicable for this change
• Code review guidelines
• Merge request performance guidelines not applicable for this change
• Style guides
• Database guides not applicable for this change
• Separation of EE specific content not applicable for this change

Availability and Testing

• 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 Not applicable for this change

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~~ not applicable for this change
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods not applicable for this change
• Security reports checked/validated by a reviewer from the AppSec team not applicable for this change

Related to #231179 (closed)