feat(jj): add jujutsu plugin

[nasso]

Standards checklist:

• The PR title is descriptive.
• The PR doesn't replicate another PR which is already open.
• I have read the contribution guide and followed all the instructions.
• The code follows the code style guide detailed in the wiki.
• The code is mine or it's from somewhere with an MIT-compatible license.
• The code is efficient, to the best of my ability, and does not waste computer resources.
• The code is stable and I have tested it myself, to the best of my abilities.
• If the code introduces new aliases, I provide a valid use case for all plugin users down below.

Changes:

• adds new plugin: jj
• adds completions for jj
• adds jj_prompt_template to easily make prompts (escapes %s)
• adds jj_prompt_template_raw to easily make colored prompts (does not escape %s)
• adds ZSH_THEME_JJ_IGNORE_WORKING_COPY to enable/disable passing --ignore-working-copy to jj when using jj_prompt_template(_raw). Disabled by default: --ignore-working-copy will not be passed and jj_prompt_template(_raw) will always return up-to-date information, which may be a little slower.
• adds some aliases (they try to follow existing git aliases where it makes sense)

Other comments:

maybe some themes could be patched or new ones added? i linked to a patch i made for myself of the sunaku theme that can serve as an example