Maintenance: move redundant code and functionalities in shared commons package

[saragerion]

Description of the feature request

The execution of this issue should be divided into 3 steps:

1. Vet the business logic of Logger, Tracer and Metrics utilities to identify code de-duplication opportunities. Opportunities found so far: cold-start business logic, fetching of environment variables.
2. Add that logic in commons.
3. Remove duplicated logic from the single utilities, in favour of the logic from the commons package.

Problem statement

Right now there is a number of functionalities that are repeated throughout the 3 different utilities, all with their own business logic and separated unit tests.
This is not optimal because:

• The same feature should have the same behaviour across all utilities
• This unnecessarily increases the cost of maintenance
• Code duplication inflates the libraries's size unnecessarily, with impact over the Lambda package size and consequently cold-starts

Summary of the feature

See above.

Code examples

Benefits for you and the wider AWS community

Describe alternatives you've considered

Additional context

See here:
https://github.com/awslabs/aws-lambda-powertools-typescript/blob/main/packages/logger/src/config/EnvironmentVariablesService.ts
https://github.com/awslabs/aws-lambda-powertools-typescript/blob/main/packages/logger/src/Logger.ts#L92

Related issues, RFCs

#165

N/A

[dreamorosi]

An internal RFC for centralising the cold start logic in the commons package has been created & reviewed by the team. Will be working on a PR in the coming days.