docs: service-registry-doc (#268)

* doc: initiate service_registry.md with summary, interface, and graph diagram

* doc: add sequence diagram for service_registry.md

* doc: update service_registry.md based on reviews

doc/src/contracts/service_registry.md

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+# Service Registry
+
+The service registry keeps track of the pool of workers that vote and sign for each chain.
+The core functionalities, such as registering a new service, worker authorization and un-authorization can only be called 
+from a governance address. Worker bonding and unbonding, as well as registering support for specific chains, are called by the worker themselves. 
+To become active and be eligible to participate in voting for a specific chain,
+each worker should first be authorized and bond enough stake, and then register support for that chain.
+Service registry is used by ampd, verifier, and multisig prover.
+
+The term `service` refers to an upper-level entity that includes several 
+`chains`. The difference is in how they are related to each other, which is 
+hierarchical; a service is like an umbrella that regulates the activities of 
+several chains that fall under its purview. The service defines common 
+parameters, such as worker requirements, bonding details, and unbonding periods, which are applicable to all associated chains. 
+Thus, we use a single instance of service registry to organize and coordinate activities across all chains.
+
+
+
+
+
+
+
+
+## Interface
+
+```Rust
+pub enum ExecuteMsg {
+    // Can only be called by governance account
+    RegisterService {
+        service_name: String,
+        service_contract: Addr,
+        min_num_workers: u16,
+        max_num_workers: Option<u16>,
+        min_worker_bond: Uint128,
+        bond_denom: String,
+        unbonding_period_days: u16,
+        description: String,
+    },
+    // Authorizes workers to join a service. Can only be called by governance account. Workers must still bond sufficient stake to participate.
+    AuthorizeWorkers {
+        workers: Vec<String>,
+        service_name: String,
+    },
+    // Revoke authorization for specified workers. Can only be called by governance account. Workers bond remains unchanged
+    UnauthorizeWorkers {
+        workers: Vec<String>,
+        service_name: String,
+    },
+
+    // Register support for the specified chains. Called by the worker.
+    RegisterChainSupport {
+        service_name: String,
+        chains: Vec<ChainName>,
+    },
+    // Deregister support for the specified chains. Called by the worker.
+    DeregisterChainSupport {
+        service_name: String,
+        chains: Vec<ChainName>,
+    },
+
+    // Locks up any funds sent with the message as stake. Called by the worker.
+    BondWorker {
+        service_name: String,
+    },
+    // Initiates unbonding of staked funds. Called by the worker.
+    UnbondWorker {
+        service_name: String,
+    },
+    // Claim previously staked funds that have finished unbonding. Called by the worker.
+    ClaimStake {
+        service_name: String,
+    },
+}
+
+```
+
+## Service Registry graph
+```mermaid
+flowchart TD
+subgraph Axelar
+    Vr{"Voting Verifier"}
+    R{"Service Registry"}
+end
+OC{"Workers"}
+
+Vr -- "GetActiveWorkers" --> R
+OC -- "De/RegisterChainSupport" --> R
+OC -- "Un/BondWorker" --> R
+OC -- "ClaimStake" --> R
+```
+
+
+## Service Registry sequence diagram
+
+```mermaid
+sequenceDiagram
+autonumber
+box LightYellow Axelar
+    participant Service Registry
+end
+actor Governance
+actor Worker
+
+Governance->>+Service Registry: Register Service
+Governance->>+Service Registry: Authorize Workers
+
+Worker->>+Service Registry: Bond Worker
+Worker->>+Service Registry: Register Chain Support
+
+```
+
+1. The Governance registers a new service by providing the necessary parameters for the service.
+2. Governance is also responsible for authorizing workers to join the service by sending an `Authorize Workers` message.
+3. Workers bond to the service, providing stake, by sending a `Bond Worker` message with appropriate funds denominator. Note that authorizing and bonding can be done in any order.
+4. Workers register support for specific chains within the service by specifying service name and chain names.
+
+
+### Notes
+1. For the process of signing, workers need to register their public key in advance to be able to participate,
+ the details of which are available in [`multisig documentation`](multisig.md).