[Improvement]: Rename TrunkBased Version Strategy to Mainline

[HHobeck]

Prerequisites

• [X] I have written a descriptive issue title
• [X] I have searched issues to ensure it has not already been reported

GitVersion package

GitVersion.Tool

GitVersion version

6.0.0-beta.7

Operating system

N/A

What are you seeing?

Rename the TrunkBased Version Strategy to Mainline because it will be conflicting with TrunkBased workflow.

What is expected?

The version strategy should be named as Mainline instead of TrunkBased.

Steps to Reproduce

Specify configuration with:

strategies:
- TrunkBased
- ConfiguredNextVersion

RepositoryFixture Test

No response

Output log or link to your CI build (if appropriate).

No response