feature: add advanced settings w/ book ID frontmatter population

[tyler-dot-earth]

SUGGESTION

Let's get #67 reviewed/merged first - it's more important - then i'll rebase this PR.

Context

This adds a good chunk of the functionality i suggested in this discord thread - primarily the ability to save the readwise book ID to frontmatter.

This is basically step 1 in improving the reliability of the plugin's sync functionality.

Issues with the current sync:

• often "loses track" of files that have gotten synced (Books disappear from booksIDsMap in data.json #68)
• filenames can change via settings on the exports config page, or when the user manually changes the name

Other notes:

• These changes do not use that ID for anything, it's purely for personal data management.
• In a future PR, I intend to integrate the now-available frontmatter book ID from this PR into the rest of the plugin's functionality so it will be preferred over the frequently buggy/out-of-sync settings.bookIDsMap
• I also intend to explore adding a Readwise: add book ID to document's frontmatter action for the command palette. I could make it appear only when the key is set in advanced settings.

Changes in this PR

• adds an Advanced settings modal, accessed via a button in the main settings menu
• adds 1 new setting: settings.frontmatterBookIdKey
  • this simply stores the frontmatter book ID the user sets in the data.json
  • this setting does NOT have a default value.
• adds 1 new button in the Advanced settings modal: Populate
  • when used, this action populates the readwise-exported notes' frontmatter with the [settings.frontmatterBookIdKey]: bookId.
  • this action will not overwrite any existing values for the given settings.frontmatterBookIdKey
  • this button is disabled when the settings.frontmatterBookIdKey is not set
  • a notice will show when population is starting and has finished

IMPORTANT NOTE ❗ 👉 an even better solution than having the plugin set this field's value this would be to add a book_id variable to YAML Frontmatter template section on the Obsidian Export settings page. Then the plugin would just read from this field (not write). I'm just working with what i can do in plugin land.

Screenshots