oracle-v2.21.0

What's Changed

• Add toolchain by @guibescos in #334
• [pytests] Use poetry and cleanup python tests by @guibescos in #337
• [pyth_oracle] Allow add_product to create product metadata by @guibescos in #332
• Update README by @guibescos in #339
• Switch to oracle releases by @guibescos in #340
• Bump cargo toml for 2.21.0 by @guibescos in #341

Full Changelog: mainnet-v2.20.1...oracle-v2.21.0