chore: migrate to main as default branch

[majorgreys]

We make main the default branch.

Contributors should update their local clone:

git remote set-head origin -a

Checklist

• Change(s) are motivated and described in the PR description.
• Testing strategy is described if automated tests are not included in the PR.
• Risk is outlined (performance impact, potential for breakage, maintainability, etc).
• Change is maintainable (easy to change, telemetry, documentation).
• Library release note guidelines are followed. If no release note is required, add label changelog/no-changelog.
• Documentation is included (in-code, generated user docs, public corp docs).
• Backport labels are set (if applicable)

Reviewer Checklist

• Title is accurate.
• No unnecessary changes are introduced.
• Description motivates each change.
• Avoids breaking API changes unless absolutely necessary.
• Testing strategy adequately addresses listed risk(s).
• Change is maintainable (easy to change, telemetry, documentation).
• Release note makes sense to a user of the library.
• Reviewer has explicitly acknowledged and discussed the performance implications of this PR as reported in the benchmarks PR comment.
• Backport labels are set in a manner that is consistent with the release branch maintenance policy
• If this PR touches code that signs or publishes builds or packages, or handles credentials of any kind, I've requested a review from @DataDog/security-design-and-guidance.
• This PR doesn't touch any of that.

[pr-commenter]

Benchmarks

Benchmark execution time: 2023-11-30 21:46:17

Comparing candidate commit 6ab140b in PR branch majorgreys/2.x-main with baseline commit c89c376 in branch main.

Found 4 performance improvements and 1 performance regressions! Performance is the same for 85 metrics, 0 unstable metrics.

scenario:flasksimple-appsec-get

• 🟩 max_rss_usage [-1.331MB; -1.105MB] or [-3.699%; -3.071%]

scenario:flasksimple-appsec-post

• 🟥 execution_time [+370.765µs; +482.851µs] or [+5.859%; +7.631%]
• 🟩 max_rss_usage [-1.386MB; -1.123MB] or [-3.848%; -3.117%]

scenario:flasksimple-appsec-telemetry

• 🟩 max_rss_usage [-1.235MB; -1.039MB] or [-3.507%; -2.951%]

scenario:span-add-metrics

• 🟩 max_rss_usage [-20.836MB; -20.671MB] or [-33.262%; -32.998%]

[P403n1x87]

Should there be a change for the test image building as well? Or is/was that done in another PR?