ocm config support

[fabianburth]

What this PR does / why we need it: This PR enables the landscaper to consume ocm config data that is usually configured in ocm config files (located at $HOME/.ocmconfig per default, if you have ocm-cli installed). For the landscaper, the ocm config data has to be specified in a config map which can be referenced in the landscaper context object. The primary purpose for enabling this is that it allows the user to specify multiple ocm repositories (called resolvers in the config file) from which the component specified in the installation and the components referenced by that component may be resolved (thus, referenced components do not necessarily have to be in the same repository, as long as the other repository is also specified as resolver).

This implementation also allows to configure credentials within this configuration data, although it is not encouraged to specify credentials in clear text in the config map. But one may specify a reference to the credentials stored somewhere else. A currently already supported method is to reference credentials stored in vault.

Which issue(s) this PR fixes: Fixes #

Special notes for your reviewer:

Release note:

[gardener-prow[bot]]

Skipping CI for Draft Pull Request. If you want CI signal for your change, please convert it to an actual PR. You can still manually trigger a test run with /test all

[gardener-robot]

@fabianburth Thank you for your contribution.

[gardener-robot]

@fabianburth You need rebase this pull request with latest master branch. Please check.

[gardener-robot]

@diaphteiros, @robertgraeff, @achimweigel, @reshnm You have pull request review open invite, please check

[fabianburth]

added documentation in the usage documentation of the landscaper context