Create a SearchSelectorField to replace the current SelectorField for adding skills

[twilkhoo]

Ticket link

Closes #502

Implementation description

• Added a new component, "SearchSelectorField"
• The component allows users to type and select existing skills, but also allows them to add new skills
• New user-added skills are first stored in a set, from which if they are deleted (volunteer changes their mind), they are removed from the set
• Skills are only added to the db when user submits

Steps to test

1. Login as any user and edit profile
2. Add skills using the new SearchSelectorField component, which includes selecting existing skills and creating new ones
3. Save changes, if testing with the firebase hosting link you may get an authentication error since backend changes don't show in the preview
4. To verify the skills are saved to the db, you can run the contents of this branch locally

What should reviewers focus on?

• Ensure that the component works as expected
• Please pay attention to minor details too: if a user types a skill that already exists, the option to add that skill disappears. The user input is formatted to titlecase (and trimmed). Clicking in the dropdown keeps the dropdown open, but clicking outside closes it.
• Lmk if there's anything that can be made more intuitive

Checklist

• [x] My PR name is descriptive and in imperative tense
• [x] My commit messages are descriptive and in imperative tense. My commits are atomic and trivial commits are squashed or fixup'd into non-trivial commits
• [x] I have run the appropriate linter(s)
• [x] I have requested a review from the PL, as well as other devs who have background knowledge on this PR or who will be building on top of this PR

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Visit the preview URL for this PR (updated for commit 25ee0d0):

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[twilkhoo]

Regarding the acronyms comment, I suppose that is a limitation with converting everything to title case. If we were to avoid converting to title case however, we would likely have lots of case differences in the db (some users may enter things all lowercase, some all uppercase, etc.). Due to this, I think that keeping the title case conversion outweighs the downsides.