add-forge-now: Allow max_pages choice with staging preset

When staging preset is used, the max_pages argument is always overwritten:

Test before modifications

swh@95e644cdaf0e:/$ swh scheduler -C $SWH_CONFIG_FILENAME \
  add-forge-now --preset staging \
  register-lister gitlab \
    instance=git.iem.at \
    max_pages=1
{'instance': 'git.iem.at', 'max_pages': 1}
{'instance': 'git.iem.at', 'max_pages': 3, 'max_origins_per_page': 10, 'enable_origins': False}
Created 1 tasks

Task 1
  Next run: today (2023-11-22T09:32:26.226019+00:00)
  Interval: 90 days, 0:00:00
  Type: list-gitlab-full
  Policy: oneshot
  Args:
  Keyword args:
    enable_origins: False
    instance: 'git.iem.at'
    max_origins_per_page: 10
    max_pages: 3

swh@95e644cdaf0e:/$ swh scheduler -C $SWH_CONFIG_FILENAME origin check-listed-origins gitlab git.iem.at -l
url                                                                       last_seen                         last_update
------------------------------------------------------------------------  --------------------------------  --------------------------------
https://git.iem.at/cm/diyremin.git                                        2023-11-22 09:32:33.388019+00:00  2021-12-14 19:08:00.541000+00:00
[...]
https://git.iem.at/zmoelnig/VeSTige.git                                   2023-11-22 09:32:32.101888+00:00  2023-09-21 05:51:13.928000+00:00

Forge git.iem.at (gitlab) has 30 listed origins in the scheduler database.

These modifications will be very useful in the add-forge-now processing requests in term of time and resources.
Check 10 origins ingestion in staging will be enough , IMHO.

Test with modifications

swh@b7559d725a59:/$ swh scheduler -C $SWH_CONFIG_FILENAME \
  add-forge-now --preset staging \
  register-lister gitlab \
    instance=git.iem.at \
    max_pages=1
{'instance': 'git.iem.at', 'max_pages': 1}
{'instance': 'git.iem.at', 'max_pages': 1, 'max_origins_per_page': 10, 'enable_origins': False}
Created 1 tasks

Task 2
  Next run: today (2023-11-22T09:22:06.800213+00:00)
  Interval: 90 days, 0:00:00
  Type: list-gitlab-full
  Policy: oneshot
  Args:
  Keyword args:
    enable_origins: False
    instance: 'git.iem.at'
    max_origins_per_page: 10
    max_pages: 1

swh@b7559d725a59:/$ swh scheduler -C $SWH_CONFIG_FILENAME origin check-listed-origins gitlab git.iem.at -l
url                                             last_seen                         last_update
----------------------------------------------  --------------------------------  --------------------------------
https://git.iem.at/pd/iemguts.git               2023-11-22 09:22:27.088210+00:00  2023-07-07 15:11:26.293000+00:00

https://git.iem.at/zmoelnig/DVImatrix848.git    2023-11-22 09:22:27.088210+00:00  2023-06-22 19:45:50.147000+00:00

Forge git.iem.at (gitlab) has 10 listed origins in the scheduler database.

swh/scheduler/cli/add_forge_now.py

@@ -58,8 +58,8 @@ def register_lister_cli(
 
     \b
     - staging preset: a single oneshot full listing task is scheduled. This "full"
-      listing is limited to 3 pages and 10 origins per page. The origins are recorded as
-      disabled (to avoid their recurrent loading).
+      listing is limited to 3 pages (default is one) and 10 origins per page.
+      The origins are recorded as disabled (to avoid their recurrent loading).
     - production preset: a recurrent full and incremental (if the loader has such a
       task) listing task are scheduled. The first run of the full lister is scheduled
       immediately, and the first run of the incremental lister is delayed by a day.
@@ -86,12 +86,24 @@ def register_lister_cli(
 
     (args, kw) = parse_options(options)
 
+    if "max_pages" in kw:
+        if kw["max_pages"] <= 3:
+            max_pages = kw["max_pages"]
+    else:
+        max_pages = 1
+
     # Recurring policy on production
     if preset == "production":
         policy = "recurring"
     else:  # staging, "full" but limited listing as a oneshot
         policy = "oneshot"
-        kw.update({"max_pages": 3, "max_origins_per_page": 10, "enable_origins": False})
+        kw.update(
+            {
+                "max_pages": max_pages,
+                "max_origins_per_page": 10,
+                "enable_origins": False,
+            }
+        )
         # We want a "full" listing in production if both incremental and full exists
         if "full" in task_types:
             task_types.pop("incremental", None)