Implement the `secrets install` command

[aryanjassal]

Specification

The cp command can copy secrets across local file system and a vault seamlessly. However, cp will not create target directories if they don't exist. More importantly, the file permissions would probably be the default permissions, something like this '-rw-r--r--'. This might not be what is desired.

This is solved by using the install command, which is able to create target directories if they don't exist (with a flag, -D --directories), and is able to set file permissions immediately on egress from the vault using the -m --mode flag. This can all be probably extended to take either an octal permission (like 755) or a string (like rw-rw-r--).

Additional context

Tasks

1. Create secrets install
2. Implement option install --directories
3. Implement egress permissions (--mode)

[linear]

ENG-503 Implement the `secrets install` command