Rename AccountsDb plugins to Geyser plugins (#23604)

geyser-plugin-interface/README.md

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+<p align="center">
+  <a href="https://solana.com">
+    <img alt="Solana" src="https://i.imgur.com/IKyzQ6T.png" width="250" />
+  </a>
+</p>
+
+# Solana Geyser Plugin Interface
+
+This crate enables an plugin to be added into the Solana Validator runtime to
+take actions at the time of account updates or block and transaction processing;
+for example, saving the account state to an external database. The plugin must
+implement the `GeyserPlugin` trait. Please see the detail of the
+`geyser_plugin_interface.rs` for the interface definition.
+
+The plugin should produce a `cdylib` dynamic library, which must expose a `C`
+function `_create_plugin()` that instantiates the implementation of the
+interface.
+
+The https://github.com/solana-labs/solana-accountsdb-plugin-postgres repository
+provides an example of how to create a plugin which saves the accounts data into
+an external PostgreSQL databases.
+
+More information about Solana is available in the [Solana documentation](https://docs.solana.com/).
+
+Still have questions?  Ask us on [Discord](https://discordapp.com/invite/pquxPsq)