Add lint

[swtwsk]

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Keep in mind:

• Documentation updates
• Changelog updates

[swtwsk]

Marked as draft for now, as there are problems with variables in SQLFluff. Added a comment to the issue in SQLFluff repo about that, hopefully it will get resolved soon.

[swtwsk]

To remove when copier is updated

[swtwsk]

The code for the dp lint command is present in this PR. However, it cannot be used yet because of arise of the dependency hell — SQLFluff uses newest version of the regex library (although for now, it does not specify it (just regex = *) so the incompatibility can be missed at the build time) while copier in the 5.1.0 version requires regex to be in 2020 version, causing SQLFluff to fail at runtime.

Right now in the PR we reference the private fork of the copier (https://github.com/swtwsk/copier/tree/regex-update) that has an updated reference. However, it is not a maintainable solution, hence the decision to stop working on dp lint for now. People responsible of copier are working on the new 6.0.0 version that will not have such an outdated dependency; on the other hand, it will be using Jinja2 > 3.0, which is unsupported by dbt for now. In order to introduce dp lint correctly, we shall wait for both dbt and copier updates that will eventually get compatible.