[vercel_team_config] Fix saml dsync for access groups

[kitfoster]

At the moment, the vercel_team_config resource incorrectly implements Access Group support. If a team has SAML roles mapped access groups, the provider deletes the mappings.

This PR fixes the access group mappings for SAML Roles.

The change is breaking 👇 @dglsparsons @jarneson let me know what you think is the best way forward with the breaking changes. Would it be sufficient to rename roles?

// before
{
	"roles": schema.MapAttribute{
		Description: "Directory groups to role or access group mappings.",
		Computed:    true,
		ElementType: types.StringType,
	},
	"access_group_id": schema.StringAttribute{
		Description: "The ID of the access group to use for the team.",
		Computed:    true,
	}
}

// after
{
	"roles": schema.MapAttribute{
		Description: "Directory groups to role or access group mappings. For each directory key, either a role or access group id is specified. The role is one of 'MEMBER', 'OWNER', 'VIEWER', 'DEVELOPER', 'BILLING' or 'CONTRIBUTOR'. The access group id is the id of an access group.",
		Computed:    true,
		ElementType: types.ObjectType{
			AttrTypes: map[string]attr.Type{
				"role":            types.StringType,
				"access_group_id": types.StringType,
			},
		},
	},
}

[kitfoster]

I would like to add a validator that exactly one of role or access_group_id is present, but couldn't make it work

[jarneson]

i think this just ends up being a marshalling error when we go to hit the RPCs? we could explicitly check it, not sure if terraform provides a hook for that. doug knows way more than I do on this stuff.

[jarneson]

any is pretty gnarly here, when we just need to support marshaling, a union type is only a few more lines of code.

[kitfoster]

Nice, how do I do the union type?

[jarneson]

something like:

type UpdatSamlConfigRole struct {
  Role *string
  AccessGroupID *string
}

func (r *UpdateSamlConfigRole) MarshalJSON() ([]byte, error) {
  if r.Role != nil { return json.Marshal(*r.Role) }
  if r.AccessGroupID != nil { return json.Marshal(*r.AccessGroupID) }
  return nil, fmt.Errorf("bad union")
}