Split character limits between local and remote notes (resolves #723)

What does this PR do?

• Add new maxRemoteNoteLength config to separately limit the length of notes from remote instances.
• Add new maxCwLength config to separately limit the length of content warnings.
• Add new maxRemoteCwLength config to separately limit the length of content warnings from remote instances.
• Add new maxAltTextLength config to separately limit the length of media descriptions.
• Add new maxRemoteAltTextLength config to separately limit the length of media descriptions from remote instances.
• Remove obsolete MAX_NOTE_TEXT_LENGTH, DB_MAX_NOTE_TEXT_LENGTH, and DB_MAX_IMAGE_COMMENT_LENGTH constants.
• Remove hardcoded OpenAPI limit on CW length.

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