Add utility functions to slsutil module

[amendlik]

What does this PR do?

Add two utility functions to the slsutil execution module. These functions are for convenience when creating template files.

Banner

slsutil.banner creates a standard warning banner like this:

        ########################################################################
        #                                                                      #
        #              THIS FILE IS MANAGED BY SALT - DO NOT EDIT              #
        #                                                                      #
        # The contents of this file are managed by Salt. Any changes to this   #
        # file may be overwritten automatically and without warning.           #
        ########################################################################

The banner is fully customizable in its content and appearance.

Boolstr

slsutil.boolstr is for converting boolean values stored in Pillar to an appropriate string representation within templated files. This can obviously be done in Jinja, but it requires an entire if/else block and managing whitespace becomes difficult.

See embedded documentation for more details.

What issues does this PR fix or reference?

None

Tests written?

Yes

Commits signed with GPG?

Yes

Please review Salt's Contributing Guide for best practices.

See GitHub's page on GPG signing for more information about signing commits with GPG.

[cachedout]

For better multi-platform support we should probably use os.linesep here instead

[amendlik]

That suggestion sounded right to me, but the documentation is making me think not:

Do not use os.linesep as a line terminator when writing files opened in text mode (the default); use a single '\n' instead, on all platforms.

It seems that Python converts \n to os.linesep when it writes out the file.

[cachedout]

The files aren't ultimately opened in text mode, though. That's the thing. :)

[s0undt3ch]

Port to master #56761

[amendlik]

@s0undt3ch Please consider bringing #53499 along with this one. It includes a few fixes to the original PR.

[s0undt3ch]

@amendlik Thank You! Will do.