Rename `Operations` menu to `Monitor`

What does this MR do?

In this MR we're renaming (behind a feature flag) the menu Operations to Monitor. We're also renaming the Settings > Operations menu item to Settings > Monitor and, finally, the breadcrumb of the page as well.

Screenshots (strongly suggested)

After the MR, the menu is like the following:

The Settings menu element is also renamed:

The breadcrumb is also changed:

Does this MR meet the acceptance criteria?

Conformity

• I have included a changelog entry, or it's not needed. (Does this MR need a changelog?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• 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.

Related to #322790 (closed)