Issue:
Todo redis interface

## Type of Change
<!-- Put an `x` in the boxes that apply -->
- [x] Enhancement

## Description
This PR is a part of greater refactoring which aims on removing `// TODO: ...` & `// FIXME: ..` from the entire codebase.
The objective of this PR is to fix `xgroup_create` by adding a guard or some specific `RedisEntryId` while also adding unit tests for the same. It also adds crate documentation for the `redis_interface` crate
<!-- Describe your changes in detail -->


### Additional Changes

- [ ] This PR modifies the database schema
- [ ] This PR modifies application configuration/environment variables

<!-- 
Provide links to the files with corresponding changes.

Following are the paths where you can find config files:
1. `config`
2. `crates/router/src/configs`
3. `loadtest/config`
-->


## Motivation and Context
The codebase wide initiative in fixing existing problems, `TODO:`s and `FIXME:`s while also adding documentations.
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## How did you test it?
unit-tests included
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## Checklist
<!-- Put an `x` in the boxes that apply -->

- [x] I formatted the code `cargo +nightly fmt`
- [x] I addressed lints thrown by `cargo clippy`
- [x] I reviewed submitted code
- [x] I added unit tests for my changes where possible

Resolution:
<think>
PR Context:
- Title: fix: resolve `TODO` comments in storage models crate
- Merged: 2022-12-15T13:40:02Z
- Files changed: 13 files
- Commits: 8 commits

Implementation approach:
## Type of Change
<!-- Put an `x` in the boxes that apply -->

- [x] Enhancement

## Description
The PR aims to resolve `TODO`'s and `FIXME`'s from the crate `strorage_models`
<!-- Describe your changes in detail -->


### Additional Changes

- [ ] This PR modifies the database schema
- [ ] This PR modifies application configuration/environment variables

<!-- 
Provide links to the files with corresponding changes.

Following are the paths where you can find config files:
1. `
</think>

To implement this, you'll need to modify:


**Detailed Implementation:**


**Commit 1:** fix: resolve `TODO` comments in storage models crate (#151)
Files to modify:


**crates/common_utils/src/lib.rs**
  Add:
    - function: pub::convert_to_pdt
    - struct: pub::Milliseconds

**crates/router/src/db/process_tracker.rs**
  Modify existing code

**crates/router/src/scheduler/consumer.rs**
  Modify existing code

**crates/router/src/scheduler/utils.rs**
  Modify existing code

**crates/router/src/types/storage/process_tracker.rs**
  Modify existing code

**crates/storage_models/src/address.rs**
  Remove:
    - function: private::convert_to_pdt

**crates/storage_models/src/payment_intent.rs**
  Modify existing code

**crates/storage_models/src/process_tracker.rs**
  Remove:
    - struct: pub::Milliseconds

**crates/storage_models/src/query/payment_attempt.rs**
  Modify existing code

**crates/storage_models/src/query/process_tracker.rs**
  Modify existing code

**crates/storage_models/src/query/refund.rs**
  Modify existing code