[PM-23379] custom fields: hide or show move up or down actions depending on the items' index

[gabrbrand]

📔 Objective

Currently move up and down actions are displayed for all custom fields, although no action is triggered in some scenarios.
This PR hides the corresponding action, if it's not needed for the specific field.

• When only one custom field is present no move actions are displayed.
• When two fields are added only move down for the first or move up for the last is displayed.
• When there are three or more items both actions are displayed for fields between the first and the last.

📸 Screenshots

⏰ Reminders before review

• Contributor guidelines followed
• All formatters and local linters executed and passed
• Written new unit and / or integration tests where applicable
• Protected functional changes with optionality (feature flags)
• Used internationalization (i18n) for all UI strings
• CI builds passed
• Communicated to DevOps any deployment requirements
• Updated any necessary documentation (Confluence, contributing docs) or informed the documentation team

🦮 Reviewer guidelines

• 👍 (:+1:) or similar for great changes
• 📝 (:memo:) or ℹ️ (:information_source:) for notes or general info
• ❓ (:question:) for questions
• 🤔 (:thinking:) or 💭 (:thought_balloon:) for more open inquiry that's not quite a confirmed issue and could potentially benefit from discussion
• 🎨 (:art:) for suggestions / improvements
• ❌ (:x:) or ⚠️ (:warning:) for more significant problems or concerns needing attention
• 🌱 (:seedling:) or ♻️ (:recycle:) for future improvements or indications of technical debt
• ⛏ (:pick:) for minor or nitpick changes

[CLAassistant]

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[CLAassistant]

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[bitwarden-bot]

Thank you for your contribution! We've added this to our internal tracking system for review.
ID: PM-23379
Link: https://bitwarden.atlassian.net/browse/PM-23379

Details on our contribution process can be found here: https://contributing.bitwarden.com/contributing/pull-requests/community-pr-process.