Enable Go nil pointer linting, and consider other opportunities to improve linting.

[lukeheath]

Goal

User story
As a Fleet contributor,
I want to eliminate nil pointer dereference issues at runtime and add additional linting checks
to improve Fleet quality.

Proposal: Use NilAway with golangci-lint v2 incremental run --new-from-rev=origin/${{ github.base_ref }}, which would be an additional golangci-lint run.

• switches -include-pkgs="github.com/fleetdm/fleet/v4" -test=false

We would have 2 golangci-lint runs. One catches all issues globally, and one (with a different set of linters) only catching issues on incremental changes. The goal would be to eventually move all linters from the incremental check to the global check.

Evaluate other linters:

• modernize!!!
• bodyclose: Checks whether HTTP response body is closed successfully.
• noctx: Detects function and method with missing usage of context.Context.
• forbidigo fmt\.Print.*(# Do not commit print statements\.)?
• errorlint: Find code that can cause problems with the error wrapping scheme introduced in Go 1.13.
• testifylint: Checks usage of github.com/stretchr/testify.
• exhaustive: Check exhaustiveness of enum switch statements.
• errchkjson: Checks types passed to the json encoding functions. Reports unsupported types and reports occurrences where the check for the returned error can be omitted.
• bidichk: Checks for dangerous unicode character sequences.

Roadmap item

Original requests

Context

• Product Designer: @getvictor
• Engineer: _________________________

Changes

Product

• NA

Engineering

• Update CI pipeline

ℹ️  Please read this issue carefully and understand it. Pay special attention to UI wireframes, especially "dev notes".

QA

NA

Test plan

NA

[sharon-fdm]

Estimated 3 points as a timebox, starting with the nil pointers first.