Improve error message if data dir and config unavailable due to permissions

[stevenGravy]

addresses #10032 where user gets very cryptic error message if running w/o rights to data dir.

If a user starts teleport and the process is running without rights to create the data dir or maintain file in data dir will now get this message.

ERRO             Teleport process must have rights to maintain files in data directory: /var/lib/teleport. Run as root or with sudo if not running as process that can maintain that directory.  service/service.go:664

[zmb3]

We really should be confirming that this is actually a permission error before we log this error. Something like:

if errors.Is(err, fs.ErrPermission) {
    ...

As for the error message, how about something as simple as:

Teleport does not have permission to write to <dir>. Ensure that you are running as a user with appropriate permissions.

[stevenGravy]

We really should be confirming that this is actually a permission error before we log this error. Something like:

if errors.Is(err, fs.ErrPermission) {
    ...

As for the error message, how about something as simple as:

Teleport does not have permission to write to <dir>. Ensure that you are running as a user with appropriate permissions.

Thanks @zmb3 I have set this as the output and permission error handling. I also modified so that if the user can't access the /etc/teleport.yaml they get more context on what the file is for. It also only gives the permissions message after checking the permission error match.

Before:

ERROR: failed to open file: /etc/teleport.yamlold
open /etc/teleport.yamlold: permission denied

Updated to:

ERROR: failed to open file for Teleport configuration: /etc/teleport.yamlold. Ensure that you are running as a user with appropriate permissions. 

[zmb3]

Just a couple minor comments.