Add gitops-update Pipeline parameter to support a custom target git branch

[LaVLaS]

Description

Introduce a parameter to the gitop-update-pipeline to allow users to specify a target branch name for the automated PR pipeline. The default value is still main but this will allow a PipelineRun to target custom branch like my-edge-demo

How Has This Been Tested?

I deployed this fix locally as part of the ai-edge demo that was using a new branch that was created from main

Merge criteria:

No issues with the parameter and the documentation is clear

• The commits are squashed in a cohesive manner and have meaningful messages.
• Testing instructions have been added in the PR body (for PRs involving changes that are not immediately obvious).
• The developer has manually tested the changes and verified that the changes work

[piotrpdev]

Suggested change

	NOTE: If you are using a branch other than `main` for your gitops workflow, you will need to modify the `PipelineRuns` examples under `tekton/gitops-update-pipeline/example-pipelineruns/` to set the `gitRepoBranchBase` parameter to your custom branch name
	> **Note**
	> If you are using a branch other than `main` for your gitops workflow, you will need to modify the `PipelineRuns` examples under `tekton/gitops-update-pipeline/example-pipelineruns/` to set the `gitRepoBranchBase` parameter to your custom branch name

Looks better:

Note
If you are using a branch other than main for your gitops workflow, you will need to modify the PipelineRuns examples under tekton/gitops-update-pipeline/example-pipelineruns/ to set the gitRepoBranchBase parameter to your custom branch name

[grdryn]

Suggested change

	NOTE: If you are using a branch other than `main` for your gitops workflow, you will need to modify the `PipelineRuns` examples under `tekton/gitops-update-pipeline/example-pipelineruns/` to set the `gitRepoBranchBase` parameter to your custom branch name
	> [!NOTE]
	> If you are using a branch other than `main` for your gitops workflow, you will need to modify the `PipelineRuns` examples under `tekton/gitops-update-pipeline/example-pipelineruns/` to set the `gitRepoBranchBase` parameter to your custom branch name

@piotrpdev Reading between the lines of the update from 21 July 2023 in the description of this issue, my understanding is that this is the more up-to-date syntax for this beta feature, and will replace the older syntax that you suggested. It says that "the old syntax will continue to work for some time", which I read as "we're not going to support the old syntax forever".

[grdryn]

Suggested change

	NOTE: If you are using a branch other than `main` for your gitops workflow, you will need to modify the `PipelineRuns` examples under `tekton/gitops-update-pipeline/example-pipelineruns/` to set the `gitRepoBranchBase` parameter to your custom branch name
	> [!NOTE]
	> If you are using a branch other than `main` for your gitops workflow, you will need to modify the `PipelineRuns` examples under `tekton/gitops-update-pipeline/example-pipelineruns/` to set the `gitRepoBranchBase` parameter to your custom branch name

@piotrpdev Reading between the lines of the update from 21 July 2023 in the description of this issue, my understanding is that this is the more up-to-date syntax for this beta feature, and will replace the older syntax that you suggested. It says that "the old syntax will continue to work for some time", which I read as "we're not going to support the old syntax forever".

[adelton]

Looks good.

It would be even nicer if the pipeline could default to the primary branch without having it specified manually but that would likely need to be a change in https://github.com/tektoncd/catalog/tree/main/task/github-open-pr/0.2 to do an extra API call to figure out the base branch if not specified.

[grdryn]

Merging this as it has 2 approvals. Suggestion can be optionally added asynchronously.

[adelton]

I've filed #141 to get the same done for the ACM part.