fix(als): deprecate als in favour of a separate plugin (#3277)

To move towards the goal of having lsp configs decentralised
and lower the maintenance burden on current maintainers, as
requested by @glepnir, @mjlbach and @justinmk

See #1693
and #1683
and #3275 (comment)

lua/lspconfig/server_configurations/als.lua

@@ -10,6 +10,10 @@ return {
     cmd = { bin_name },
     filetypes = { 'ada' },
     root_dir = util.root_pattern('Makefile', '.git', '*.gpr', '*.adc'),
+    deprecate = {
+      to = 'github.com/TamaMcGlinn/nvim-lspconfig-ada',
+      version = '0.2.0',
+    },
   },
   docs = {
     description = [[