ER: Make current_skills a many-to-many with a new skills table

### Overview
Suggestion from a PR review. The suggestion is to make the user table's current_skills into a many to many relationship to a skills table that contain all the skills.

### Action Items
- [ ] discussion
- [ ] decision and reasoning
- [ ] add a decision record

### Discussion Items
- [ ] current design
- [ ] proposed design
- [ ] advantages/disadvantages

### Resources/Instructions

- original comment

>255 characters doesn't seem like enough space. My inclination is to make this a many to many to make it easier to locate people with specific skills. The only problem is it may be tough to come up with the list of skills. If you are not going to take the current and target skills and make them a mapping to a skills table, then I suggest you make this (and target_skills) into a TextField so you don't have to worry about its length.

_Originally posted by @cnk in https://github.com/hackforla/peopledepot/pull/83#discussion_r985363106_

- current design
- free-form text entry. Supports prose as well as keywords
- many to many with skills table
- allows fast searching based on skills
- cleaner design
- force keyword entry