Ability to control/change commit message of bootstrap

[gibbonsjohnm]

At my company, we have strict commit message requirements that enforce the use of a certain prefix (e.g. !000 - Commit message) in order to push. It would be nice to have the ability to either be able to add a prefix to the default flux bootstrap commit message (similar to how --commit-message-appendix works) or have full control over the message entirely. Currently, we are blocked from using the recommended way to deploy flux.

[felixk101]

#1350 contains a possible fix for this issue

[sereinity]

As said in fluxcd/terraform-provider-flux#550, it would be great if those new options can make commits match conventional commits convention.