Generated flag manifest file should end with final newline

[sahidvelji]

This might be a bit of a nit, but text files should end with a newline character.

> openfeature manifest add enableMagicButton --type boolean --default-value false --description "Activates a special button that enhances user interaction with magical, intuitive functionalities."
 SUCCESS  Flag 'enableMagicButton' added successfully to flags.json
❯ od -c flags.json
0000000    {  \n           "   $   s   c   h   e   m   a   "   :       "
0000020    h   t   t   p   s   :   /   /   r   a   w   .   g   i   t   h
0000040    u   b   u   s   e   r   c   o   n   t   e   n   t   .   c   o
0000060    m   /   o   p   e   n   -   f   e   a   t   u   r   e   /   c
0000100    l   i   /   r   e   f   s   /   h   e   a   d   s   /   m   a
0000120    i   n   /   s   c   h   e   m   a   /   v   0   /   f   l   a
0000140    g   -   m   a   n   i   f   e   s   t   .   j   s   o   n   "
0000160    ,  \n           "   f   l   a   g   s   "   :       {  \n
0000200                "   e   n   a   b   l   e   M   a   g   i   c   B
0000220    u   t   t   o   n   "   :       {  \n
0000240    "   d   e   f   a   u   l   t   V   a   l   u   e   "   :
0000260    f   a   l   s   e   ,  \n                           "   d   e
0000300    s   c   r   i   p   t   i   o   n   "   :       "   A   c   t
0000320    i   v   a   t   e   s       a       s   p   e   c   i   a   l
0000340        b   u   t   t   o   n       t   h   a   t       e   n   h
0000360    a   n   c   e   s       u   s   e   r       i   n   t   e   r
0000400    a   c   t   i   o   n       w   i   t   h       m   a   g   i
0000420    c   a   l   ,       i   n   t   u   i   t   i   v   e       f
0000440    u   n   c   t   i   o   n   a   l   i   t   i   e   s   .   "
0000460    ,  \n                           "   f   l   a   g   T   y   p
0000500    e   "   :       "   b   o   o   l   e   a   n   "  \n
0000520            }  \n           }  \n   }
0000531

The very last byte is a } instead of \n.

The fix should be very simple. Just append the byte '\n' before writing the manifest to a file.

I believe it should be done here:

cli/internal/manifest/manage.go

Lines 155 to 160 in 6cb2453

	// writeManifest marshals and writes a manifest to the given path atomically
	func writeManifest(path string, manifest *initManifest) error {
	formattedManifest, err := json.MarshalIndent(manifest, "", " ")
	if err != nil {
	return err
	}

	formattedManifest = append(formattedManifest, '\n')