[Feature] Add Dropbox loader (#1073)

Co-authored-by: Deshraj Yadav <deshrajdry@gmail.com>

pyproject.toml

@@ -147,6 +147,7 @@ newspaper3k = { version = "^0.2.8", optional = true }
 listparser = { version = "^0.19", optional = true }
 google-generativeai = { version = "^0.3.0", optional = true }
 modal = { version = "^0.56.4329", optional = true }
+dropbox = { version = "^11.36.2", optional = true }
 
 [tool.poetry.group.dev.dependencies]
 black = "^23.3.0"
@@ -214,6 +215,7 @@ rss_feed = [
 ]
 google = ["google-generativeai"]
 modal = ["modal"]
+dropbox = ["dropbox"]
 
 [tool.poetry.group.docs.dependencies]