refactor: architecture documentation

[raulb]

Description

• Leaves https://conduit.io/docs/getting-started/architecture as the main source of truth when it comes architecture information, referencing that one from the README.
• Creates a separate page for the pkg structure to not lose that information that's relevant to this repository.

Quick checks:

• I have followed the Code Guidelines.
• There is no other pull request for the same update/change.
• I have written unit tests.
• I have made sure that the PR is of reasonable size and can be easily reviewed.

[hariso]

Thanks for this @raulb ! WDYT about leaving a link to the architecture page somewhere in this repo (e.g. README)?

[raulb]

Thanks for this @raulb ! WDYT about leaving a link to the architecture page somewhere in this repo (e.g. README)?

@hariso It's there! https://github.com/ConduitIO/conduit/pull/1732/files#diff-b335630551682c19a781afebcf4d07bf978fb1f8ac04c6bf87428ed5106870f5R293

[hariso]

Thanks for this @raulb ! WDYT about leaving a link to the architecture page somewhere in this repo (e.g. README)?

@hariso It's there! https://github.com/ConduitIO/conduit/pull/1732/files#diff-b335630551682c19a781afebcf4d07bf978fb1f8ac04c6bf87428ed5106870f5R293

Sorry, missed it!