Feat/add leveled logger interface

[Pokom]

Add base level log There are two main requirements for improving the logging of cloudcost-exporter:

1. Structured logging with consistent labels across providers and collectors
2. Ability to define a log level and runtime that limits the logs

There are no shortage of existing Go packages that could have been to meet the first requirement, such that:

• [logrus](https://pkg.go.dev/github.com/sirupsen/
• zap
• [zerolog](https://github.com/

However each of these comes with tradeoffs and then yet dependency to maintain. The go team released slog officially in go 1.21, which provides a structured logging implemention as part of the standard library. This makes it a prime candidate to immediate meet the first requirement.

The second requirement(levels) is a bit more nuanced since the slog is thin implementation. The go team provides a reference example to use: https://pkg.go.dev/log/slog@master#example-Handler-LevelHandler. This PR aims to meet both requirements by:

1. Adding slog as a common logging library to use
2. Creating a levels implementation that allows us to toggle the emitted level

There are two three methods added as well:

• GetLogLevel to convert a string to the log level
• WriterForOutput to convert a string to an io.Writer
• HandlerForOutput that takes a string and returns a slog handler for json or text