Add write support for vaultkv secrets

[MatteoVoges]

Fixes issue #786, #854

Proposed Changes

• Support writing vaultkv secrets with kapitan (refs with inventory and cli)
• New Interfaces for VaultClient and VaultServer to simplify authentication and testing a bit and reduce code redundancy.
• Update hvac to version 1.0.2 and replace depricated api functions

Examples

• ref-tag-pattern: ?{vaultkv:path/to/ref:mount_in_vault:path/in/vault:key||random:str}
• If some of the fields are not specified then following defaults get chosen:
  • e.g. tag ?{vaultkv:path/to/ref:::key||random:str} would create / lookup a secret with
    • mount=secret and
    • path/in/vault=path/to/ref

CLI

Use kapitan refs --write vaultkv:test/secret -f test/secret/file --refs-path refs/path --vault-mount testmount --vault-path test/path --vault-key testkey to write your secret stored in test/secret/file to kapitan ref engine.

Replaced / Outdated Pull-Requests:

• Add write support for vaulktkv secrets #925
• Provide client and server interface for vault #940
• Update hvac to version 1.0.2 #957

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