doc: Add troubleshooting for coverage error statuses CY-6365

[prcr]

Adds troubleshooting instructions for the possible coverage "error status" displayed on the coverage set-up page for each repository:

• Commit not found
• Branch not enabled
• Commit not analyzed
• Pending

Also moves the guidance for scenarios where the coverage value isn't displayed on the Codacy UI directly to the main section "Validating coverage" so that users don't need to navigate away from the main sequence of instructions.

:eyes: Live preview

https://feat-update-codacy-coverage-reporte--docs-codacy.netlify.app/coverage-reporter/#validating-coverage

:construction: To do

• [x] Merge https://github.com/codacy/codacy-coverage-reporter/pull/406 and https://github.com/codacy/codacy-coverage-reporter/pull/407
• [x] Move the troubleshooting table to the final location and link it from the setup validation section
• [x] Solve TODO comments
• [x] Consider improving the presentation of the troubleshooting instructions to make them more compact

[prcr]

@prcr Overall, consider giving more place between sections for readability purposes, the page looks quite condense. bow

I experimented with including all scenarios/error statuses in the same table, and I think this improves the readability of the troubleshooting section.