fix: repository ruleset failing with incorrect external-name

[xunholy]

Description of your changes

This atempts to fix the external-name with the Repository Ruleset resource as documented in issue #176 - I've had issues locally running the make commands if someone could please assist there.

Fixes #176

I have:

• Read and followed Crossplane's contribution process.
• Run make reviewable test to ensure this PR is ready for review.

How has this code been tested

[xunholy]

@AtzeDeVries I also noticed a comment from you here as I believe this should be fixed too

// We cannot use the external_name = pattern here since pattern can contain non alpha numberic characters
"github_branch_protection": config.IdentifierFromProvider,

I was thinking something like this should potentially work?

"github_branch_protection": config.TemplatedStringAsIdentifier("repository_pattern", "{{ .parameters.repository }}:{{ .parameters.pattern }}"),

[olga-mir]

@pravindahal I've noticed this PR was opened some time ago and was not reviewed by maintainers, will you be able to have a look?
I've seen the same behaviour with importing teams resources. This is quite limiting because it is difficult to adopt existing resources since numerical IDs are not easily available when we build composite resources.

[AtzeDeVries]

@olga-mir the pattern can also be something like the pattern of a branch protection can * or production/*. This would result into external_names with non alphanumeric characters, which is not allowed.
The external-name is a annotation and https://kubernetes.io/docs/concepts/overview/working-with-objects/annotations/#syntax-and-character-set shows that annotations can only be alphanumeric.

Also changing the external name pattern is a breaking change.

[AtzeDeVries]

I closed this prematurely. We should still fix the rule_set external_name