Add Finnish translation

[tlindi]

Description:

Added Finnish language texts to fi-FI.json

Motivation and Context:

I provided Finnish translation improvements for Zap Android so I checked if Desktop would need translation too.
I found fi-FI.json existed but there was zero translated lines. So I filled them all.

How Has This Been Tested?

N/A

Screenshots (if appropriate):

N/A

Types of changes:

Inserted finnish translations betweeb "" 's

Checklist:

• [ X ] My code follows the code style of this project.
• [ - ] I have reviewed and updated the documentation accordingly.
• [ - ] I have read the CONTRIBUTING document.
• [ - ] I have added tests to cover my changes where needed.
• [ - ] All new and existing tests passed.
• [ - ] My commits have been squashed into a concise set of changes.
  -> is two commits Bad?

[welcome]

⚡️ Thanks for opening this pull request! ⚡️
We use conventional commits to streamline the release process. Before your pull request can be merged, you should squash your commits and reword your commit messages to follow the conventional commit message format.
Examples of commit messages with semantic prefixes:

• fix(ui): ensure search input is cleared after submit
• feat(wallet): add new transaction detail view
• perf(channels): prevent double render in channel list
  Things that will help get your PR across the finish line:
• Run yarn lint locally to catch formatting errors earlier.
• Run yarn test locally to catch test failures early.
• Run yarn extract-messages locally to extract new transaction strings.
• Document any user-facing changes you've made.
• Include tests when adding/changing behavior.
• Include screenshots and animated GIFs whenever possible.

[coveralls]

Coverage remained the same at 21.942% when pulling 0b4cfb4 on tlindi:master into 928602b on LN-Zap:master.