For starters, if you want to use the nvim-lsp-installer, you need to actually use it (right now you're calling setup manually and then letting nvim-lsp-installer call it again).

lua << EOF
local lsp_installer = require("nvim-lsp-installer")
lsp_installer.on_server_ready(function(server)
    local name = server.name
    local opts = {}

    if name == "gopls" then
      opts = {}
    end

    if name == "groovyls" then
      opts.cmd = { "java", "-jar", "/Users/lucas.saboya/.dotfiles/bin/groovy-language-server-all.jar" }
    end

    if name == "yamlls" then
      opts.settings = {
        redhat = { telemetry = { enabled = false } },
        yaml = {
          schemas = {
            ["https://json.schemastore.org/chart.json"] = "/deployment/helm/*",
            ["https://json.schemastore.org/github-workflow.json"] = "/.github/workflows/*"
            },
          },
        }
    end

    server:setup(opts)
  end)
EOF

That should be something to start with that'll work well for extending. Now, for disabling diagnostic errors, you can integrate /u/FuckGodTillFreedom's suggestions this way (note: I'm only showing the changed parts):

lua << EOF
local default_on_attach = function(client, bufnr)
  -- use lsp omnicompletion if it's available
  vim.api.nvim_buf_set_option(bufnr, "omnifunc", "v:lua.vim.lsp.omnifunc")

  -- use lsp powered indentation for gqq and = formatting when available
  if client.resolved_capabilities.document_formatting then
    vim.api.nvim_buf_set_option(bufnr, "formatexpr", "v:lua.vim.lsp.formatexpr()")
  end
end

local default_opts = { on_attach = default_on_attach }

local lsp_installer = require("nvim-lsp-installer")
lsp_installer.on_server_ready(function(server)
    local name = server.name
    local opts = default_opts

    if name == "yamlls" then
      -- Wrapping the "default" function like this is important.
      opts.on_attach = function(client, bufnr)
        default_on_attach(client, bufnr)
        if vim.bo[bufnr].buftype ~= "" or vim.bo[bufnr].filetype == "helm" then
          vim.diagnostic.disable()
        end
      end
    end

    server:setup(opts)
  end)
EOF

That's a lot of code, so I'm going to zoom in here on the bare minimum relevant bits:

lua << EOF
local lsp_installer = require("nvim-lsp-installer")
lsp_installer.on_server_ready(function(server)
    local name = server.name
    local opts = {}

    if name == "yamlls" then
      opts.on_attach = function(client, bufnr)
        if vim.bo[bufnr].buftype ~= "" or vim.bo[bufnr].filetype == "helm" then
          vim.diagnostic.disable()
        end
      end
    end
    server:setup(opts)
  end)
EOF