install: improve detection for desired install mode when creating operator group

[joelanford]

See #50 (comment)

We basically need a set intersection of:

• The install modes supported by operator (note we only know the supported install modes of the channel heads)
• The install modes compatible with the namespaces from the --watch flag.
• The install modes compatible with the namespaces watched by the existing OperatorGroup, if it exists.

After the result of that set intersection, we could use a precedence order of:

1. AllNamespaces
2. OwnNamespace
3. SingleNamespace
4. MultiNamespaces

Note that in reality, the only time we'll actually have more than one choice is if:

• the operator supports at least AllNamespaces and OwnNamespace
• the watch flag is unset
• there is no existing operator group

In that case, we would choose AllNamespaces.

SingleNamespace is only an option when --watch is explicitly set to single namespace that is different than the install namespace or an existing OperatorGroup specifies a different namespace.

MultiNamespaces is only an option when --watch is explicitly set to multiple namespaces or an existing OperatorGroup specifies multiples namespaces.

Signed-off-by: Joe Lanford [email protected]

[openshift-ci]

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[perdasilva]

/lgtm