Pg 3565 add field placeholders

[snake14]

Description:

Product wanted placeholders added to all free-form inputs so that the label is always above the input. The PR does that.

Since I was already editing the necessary Vue templates for a couple other tickets, I implemented those as part of this PR as well.

Full changes:

• Rename description fields to: Description (optional)
• Add placeholders to all text inputs so that the label is always above the field
• Move the Trigger/Variable type up next to the form title instead of being a disabled field
• Redirect to the Tag/Trigger/Variable list after a Tag/Trigger/Variable is created/updated

Internal tickets:

• PG-3565
• PG-3686
• PG-3347

Review

• [ ] Functional review done
• [ ] Potential edge cases thought about (behavior of the code with strange input, with strange internal state or possible interactions with other Matomo subsystems)
• [ ] Usability review done (is anything maybe unclear or think about anything that would cause people to reach out to support)
• [ ] Security review done
• [ ] Wording review done
• [ ] Code review done
• [ ] Tests were added if useful/possible
• [ ] Reviewed for breaking changes
• [ ] Developer changelog updated if needed
• [ ] Documentation added if needed
• [ ] Existing documentation updated if needed

[araichyk]

Maybe missing a placeholder on this one under the "Show advanced settings" in VariableEdit.vue:

https://github.com/matomo-org/tag-manager/blob/4b989af8b0e2bb288b4e21a86363092d16f2a88f/vue/src/Variable/VariableEdit.vue#L99-L106

[snake14]

Maybe missing a placeholder on this one under the "Show advanced settings" in VariableEdit.vue:

https://github.com/matomo-org/tag-manager/blob/4b989af8b0e2bb288b4e21a86363092d16f2a88f/vue/src/Variable/VariableEdit.vue#L99-L106

@araichyk Good catch. I went ahead and added one :+1: