Project to environment

[pokornyd]

Motivation

Fixes #247

• all references to project were updated to environment in properties, method names, comments and docs, if applicable

• some subscription API endpoints still refer to project, which is in line with the API specification

• some dead links in readme updated in the process

• Checklist

• [x] Code follows coding conventions held in this repo

• [ ] Automated tests have been added

• [x] Tests are passing

• [x] Docs have been updated (if applicable)

• [ ] Temporary settings (e.g. variables used during development and testing) have been reverted to defaults

How to test

Just look through the changes and see if there's some code yet to be updated

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 95.23810% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 85.30%. Comparing base (98dab71) to head (bd886e0).

Files	Patch %	Lines
Kontent.Ai.Management/ManagementClient.cs	0.00%	2 Missing and 2 partials :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #259 +/- ## ========================================== - Coverage 89.92% 85.30% -4.62% ========================================== Files 267 267 Lines 2927 2927 Branches 318 318 ========================================== - Hits 2632 2497 -135 - Misses 292 337 +45 - Partials 3 93 +90 ```

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